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 $53.40   12.756%   $60.2117   $60.21   $60.20   $60.20  
  Purchase #2 $184.82   11.484%   $206.0447   $206.04   $206.05   $206.00  
  Purchase #3 $168.85   10.331%   $186.2939   $186.29   $186.30   $186.30  
  Purchase #4 $187.88   5.817%   $198.809   $198.81   $198.80   $198.80  
  Purchase #5 $101.28   12.341%   $113.779   $113.78   $113.80   $113.80  
  Purchase #6 $83.50   4.158%   $86.9719   $86.97   $86.95   $87.00  
  Purchase #7 $121.92   8.827%   $132.6819   $132.68   $132.70   $132.70  
  7 purchase totals = $901.65       $984.7921   $984.78   $984.80   $984.80