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 $212.41   11.557%   $236.9582   $236.96   $236.95   $237.00  
  Purchase #2 $62.56   3.526%   $64.7659   $64.77   $64.75   $64.80  
  Purchase #3 $10.79   3.857%   $11.2062   $11.21   $11.20   $11.20  
  Purchase #4 $175.84   4.614%   $183.9533   $183.95   $183.95   $184.00  
  Purchase #5 $179.89   10.865%   $199.435   $199.44   $199.45   $199.40  
  Purchase #6 $32.75   11.827%   $36.6233   $36.62   $36.60   $36.60  
  Purchase #7 $195.59   8.793%   $212.7882   $212.79   $212.80   $212.80  
  7 purchase totals = $869.83       $945.7301   $945.74   $945.70   $945.80