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 $44.49   12.792%   $50.1812   $50.18   $50.20   $50.20  
  Purchase #2 $105.38   13.293%   $119.3882   $119.39   $119.40   $119.40  
  Purchase #3 $39.55   5.292%   $41.643   $41.64   $41.65   $41.60  
  Purchase #4 $108.96   6.549%   $116.0958   $116.10   $116.10   $116.10  
  Purchase #5 $158.70   5.593%   $167.5761   $167.58   $167.60   $167.60  
  Purchase #6 $233.77   13.301%   $264.8637   $264.86   $264.85   $264.90  
  Purchase #7 $229.48   13.473%   $260.3978   $260.40   $260.40   $260.40  
  7 purchase totals = $920.33       $1,020.1458   $1,020.15   $1,020.20   $1,020.20