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 $44.82   11.584%   $50.0119   $50.01   $50.00   $50.00  
  Purchase #2 $58.28   11.353%   $64.8965   $64.90   $64.90   $64.90  
  Purchase #3 $236.30   4.752%   $247.529   $247.53   $247.55   $247.50  
  Purchase #4 $176.74   4.562%   $184.8029   $184.80   $184.80   $184.80  
  Purchase #5 $132.59   4.804%   $138.9596   $138.96   $138.95   $139.00  
  Purchase #6 $181.38   12.443%   $203.9491   $203.95   $203.95   $203.90  
  Purchase #7 $64.28   9.761%   $70.5544   $70.55   $70.55   $70.60  
  7 purchase totals = $894.39       $960.7034   $960.70   $960.70   $960.70