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 $52.92   9.524%   $57.9601   $57.96   $57.95   $58.00  
  Purchase #2 $58.87   11.240%   $65.487   $65.49   $65.50   $65.50  
  Purchase #3 $240.94   11.551%   $268.771   $268.77   $268.75   $268.80  
  Purchase #4 $238.70   12.198%   $267.8166   $267.82   $267.80   $267.80  
  Purchase #5 $40.55   7.847%   $43.732   $43.73   $43.75   $43.70  
  Purchase #6 $159.68   5.792%   $168.9287   $168.93   $168.95   $168.90  
  Purchase #7 $56.46   13.450%   $64.0539   $64.05   $64.05   $64.10  
  7 purchase totals = $848.12       $936.7493   $936.75   $936.75   $936.80