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 $121.28   11.291%   $134.9737   $134.97   $134.95   $135.00  
  Purchase #2 $205.69   8.732%   $223.6509   $223.65   $223.65   $223.70  
  Purchase #3 $78.57   3.649%   $81.437   $81.44   $81.45   $81.40  
  Purchase #4 $198.69   7.579%   $213.7487   $213.75   $213.75   $213.70  
  Purchase #5 $62.56   13.455%   $70.9774   $70.98   $71.00   $71.00  
  Purchase #6 $41.95   9.744%   $46.0376   $46.04   $46.05   $46.00  
  Purchase #7 $117.76   12.491%   $132.4694   $132.47   $132.45   $132.50  
  7 purchase totals = $826.50       $903.2947   $903.30   $903.30   $903.30