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 $87.59   5.293%   $92.2261   $92.23   $92.25   $92.20  
  Purchase #2 $146.75   8.544%   $159.2883   $159.29   $159.30   $159.30  
  Purchase #3 $212.27   4.478%   $221.7755   $221.78   $221.80   $221.80  
  Purchase #4 $17.41   10.721%   $19.2765   $19.28   $19.30   $19.30  
  Purchase #5 $243.47   4.449%   $254.302   $254.30   $254.30   $254.30  
  Purchase #6 $142.84   4.355%   $149.0607   $149.06   $149.05   $149.10  
  Purchase #7 $129.83   8.531%   $140.9058   $140.91   $140.90   $140.90  
  7 purchase totals = $980.16       $1,036.8349   $1,036.85   $1,036.90   $1,036.90