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 $218.90   13.548%   $248.5566   $248.56   $248.55   $248.60  
  Purchase #2 $151.86   7.412%   $163.1159   $163.12   $163.10   $163.10  
  Purchase #3 $62.37   10.351%   $68.8259   $68.83   $68.85   $68.80  
  Purchase #4 $151.78   7.718%   $163.4944   $163.49   $163.50   $163.50  
  Purchase #5 $218.66   12.811%   $246.6725   $246.67   $246.65   $246.70  
  Purchase #6 $162.37   12.786%   $183.1306   $183.13   $183.15   $183.10  
  Purchase #7 $75.54   8.359%   $81.8544   $81.85   $81.85   $81.90  
  7 purchase totals = $1,041.48       $1,155.6503   $1,155.65   $1,155.65   $1,155.70