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 $52.56   3.831%   $54.5736   $54.57   $54.55   $54.60  
  Purchase #2 $209.96   3.566%   $217.4472   $217.45   $217.45   $217.40  
  Purchase #3 $163.27   7.434%   $175.4075   $175.41   $175.40   $175.40  
  Purchase #4 $234.85   5.504%   $247.7761   $247.78   $247.80   $247.80  
  Purchase #5 $182.55   8.827%   $198.6637   $198.66   $198.65   $198.70  
  Purchase #6 $87.58   4.299%   $91.3451   $91.35   $91.35   $91.30  
  Purchase #7 $25.54   7.403%   $27.4307   $27.43   $27.45   $27.40  
  7 purchase totals = $956.31       $1,012.6439   $1,012.65   $1,012.65   $1,012.60