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 $91.32   3.439%   $94.4605   $94.46   $94.45   $94.50  
  Purchase #2 $140.73   13.691%   $159.9973   $160.00   $160.00   $160.00  
  Purchase #3 $126.35   10.526%   $139.6496   $139.65   $139.65   $139.60  
  Purchase #4 $49.38   4.700%   $51.7009   $51.70   $51.70   $51.70  
  Purchase #5 $65.70   5.769%   $69.4902   $69.49   $69.50   $69.50  
  Purchase #6 $9.51   12.438%   $10.6929   $10.69   $10.70   $10.70  
  Purchase #7 $198.65   4.830%   $208.2448   $208.24   $208.25   $208.20  
  7 purchase totals = $681.64       $734.2362   $734.23   $734.25   $734.20