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 $104.66   10.528%   $115.6786   $115.68   $115.70   $115.70  
  Purchase #2 $66.53   3.679%   $68.9776   $68.98   $69.00   $69.00  
  Purchase #3 $48.93   7.697%   $52.6961   $52.70   $52.70   $52.70  
  Purchase #4 $136.46   5.289%   $143.6774   $143.68   $143.70   $143.70  
  Purchase #5 $169.46   12.830%   $191.2017   $191.20   $191.20   $191.20  
  Purchase #6 $250.95   7.750%   $270.3986   $270.40   $270.40   $270.40  
  Purchase #7 $83.43   8.823%   $90.791   $90.79   $90.80   $90.80  
  7 purchase totals = $860.42       $933.4210   $933.43   $933.50   $933.50