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 $113.56   5.187%   $119.4504   $119.45   $119.45   $119.50  
  Purchase #2 $55.68   11.780%   $62.2391   $62.24   $62.25   $62.20  
  Purchase #3 $242.30   12.103%   $271.6256   $271.63   $271.65   $271.60  
  Purchase #4 $32.45   12.263%   $36.4293   $36.43   $36.45   $36.40  
  Purchase #5 $67.35   11.328%   $74.9794   $74.98   $75.00   $75.00  
  Purchase #6 $64.78   6.164%   $68.773   $68.77   $68.75   $68.80  
  Purchase #7 $88.72   5.365%   $93.4798   $93.48   $93.50   $93.50  
  7 purchase totals = $664.84       $726.9766   $726.98   $727.05   $727.00