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 $245.90   5.141%   $258.5417   $258.54   $258.55   $258.50  
  Purchase #2 $123.47   11.489%   $137.6555   $137.66   $137.65   $137.70  
  Purchase #3 $60.82   5.352%   $64.0751   $64.08   $64.10   $64.10  
  Purchase #4 $56.47   5.612%   $59.6391   $59.64   $59.65   $59.60  
  Purchase #5 $229.28   6.605%   $244.4239   $244.42   $244.40   $244.40  
  Purchase #6 $15.46   11.212%   $17.1934   $17.19   $17.20   $17.20  
  Purchase #7 $94.45   7.465%   $101.5007   $101.50   $101.50   $101.50  
  7 purchase totals = $825.85       $883.0294   $883.03   $883.05   $883.00