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 $205.64   13.336%   $233.0642   $233.06   $233.05   $233.10  
  Purchase #2 $62.28   6.161%   $66.1171   $66.12   $66.10   $66.10  
  Purchase #3 $155.84   11.246%   $173.3658   $173.37   $173.35   $173.40  
  Purchase #4 $137.62   11.423%   $153.3403   $153.34   $153.35   $153.30  
  Purchase #5 $5.48   11.272%   $6.0977   $6.10   $6.10   $6.10  
  Purchase #6 $59.48   10.148%   $65.516   $65.52   $65.50   $65.50  
  Purchase #7 $92.93   6.157%   $98.6517   $98.65   $98.65   $98.70  
  7 purchase totals = $719.27       $796.1528   $796.16   $796.10   $796.20