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 $132.90   6.513%   $141.5558   $141.56   $141.55   $141.60  
  Purchase #2 $182.98   10.428%   $202.0612   $202.06   $202.05   $202.10  
  Purchase #3 $95.76   12.336%   $107.573   $107.57   $107.55   $107.60  
  Purchase #4 $111.84   5.626%   $118.1321   $118.13   $118.15   $118.10  
  Purchase #5 $29.40   9.538%   $32.2042   $32.20   $32.20   $32.20  
  Purchase #6 $141.59   11.236%   $157.4991   $157.50   $157.50   $157.50  
  Purchase #7 $240.52   8.738%   $261.5366   $261.54   $261.55   $261.50  
  7 purchase totals = $934.99       $1,020.5620   $1,020.56   $1,020.55   $1,020.60