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 $204.77   5.871%   $216.792   $216.79   $216.80   $216.80  
  Purchase #2 $177.57   6.635%   $189.3518   $189.35   $189.35   $189.40  
  Purchase #3 $117.85   5.845%   $124.7383   $124.74   $124.75   $124.70  
  Purchase #4 $155.84   4.573%   $162.9666   $162.97   $162.95   $163.00  
  Purchase #5 $24.40   3.157%   $25.1703   $25.17   $25.15   $25.20  
  Purchase #6 $91.41   10.664%   $101.158   $101.16   $101.15   $101.20  
  Purchase #7 $110.48   10.632%   $122.2262   $122.23   $122.25   $122.20  
  7 purchase totals = $882.32       $942.4032   $942.41   $942.40   $942.50