Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.58   8.776%   $264.9566   $264.96   $264.95   $265.00  
  Purchase #2 $221.31   12.423%   $248.8033   $248.80   $248.80   $248.80  
  Purchase #3 $193.60   11.364%   $215.6007   $215.60   $215.60   $215.60  
  Purchase #4 $200.57   4.377%   $209.3489   $209.35   $209.35   $209.30  
  Purchase #5 $249.94   12.564%   $281.3425   $281.34   $281.35   $281.30  
  Purchase #6 $194.67   10.115%   $214.3609   $214.36   $214.35   $214.40  
  Purchase #7 $218.96   3.494%   $226.6105   $226.61   $226.60   $226.60  
  7 purchase totals = $1,522.63       $1,661.0234   $1,661.02   $1,661.00   $1,661.00