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 $218.61   12.230%   $245.346   $245.35   $245.35   $245.30  
  Purchase #2 $75.49   7.784%   $81.3661   $81.37   $81.35   $81.40  
  Purchase #3 $236.69   7.465%   $254.3589   $254.36   $254.35   $254.40  
  Purchase #4 $205.57   3.854%   $213.4927   $213.49   $213.50   $213.50  
  Purchase #5 $118.73   12.477%   $133.5439   $133.54   $133.55   $133.50  
  Purchase #6 $199.96   12.294%   $224.5431   $224.54   $224.55   $224.50  
  Purchase #7 $40.54   13.324%   $45.9415   $45.94   $45.95   $45.90  
  7 purchase totals = $1,095.59       $1,198.5922   $1,198.59   $1,198.60   $1,198.50