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 $206.39   13.716%   $234.6985   $234.70   $234.70   $234.70  
  Purchase #2 $240.93   13.280%   $272.9255   $272.93   $272.95   $272.90  
  Purchase #3 $228.60   8.437%   $247.887   $247.89   $247.90   $247.90  
  Purchase #4 $214.87   13.502%   $243.8817   $243.88   $243.90   $243.90  
  Purchase #5 $89.85   8.512%   $97.498   $97.50   $97.50   $97.50  
  Purchase #6 $152.56   4.632%   $159.6266   $159.63   $159.65   $159.60  
  Purchase #7 $153.47   5.242%   $161.5149   $161.51   $161.50   $161.50  
  7 purchase totals = $1,286.67       $1,418.0322   $1,418.04   $1,418.10   $1,418.00