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 $108.55   8.773%   $118.0731   $118.07   $118.05   $118.10  
  Purchase #2 $155.27   9.266%   $169.6573   $169.66   $169.65   $169.70  
  Purchase #3 $87.85   13.152%   $99.404   $99.40   $99.40   $99.40  
  Purchase #4 $191.96   7.314%   $206   $206.00   $206.00   $206.00  
  Purchase #5 $32.43   6.156%   $34.4264   $34.43   $34.45   $34.40  
  Purchase #6 $135.49   6.863%   $144.7887   $144.79   $144.80   $144.80  
  Purchase #7 $19.39   11.421%   $21.6045   $21.60   $21.60   $21.60  
  7 purchase totals = $730.94       $793.9540   $793.95   $793.95   $794.00