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 $85.81   8.413%   $93.0292   $93.03   $93.05   $93.00  
  Purchase #2 $226.65   13.233%   $256.6426   $256.64   $256.65   $256.60  
  Purchase #3 $32.27   8.490%   $35.0097   $35.01   $35.00   $35.00  
  Purchase #4 $206.30   13.676%   $234.5136   $234.51   $234.50   $234.50  
  Purchase #5 $30.82   11.725%   $34.4336   $34.43   $34.45   $34.40  
  Purchase #6 $158.79   8.255%   $171.8981   $171.90   $171.90   $171.90  
  Purchase #7 $78.74   5.550%   $83.1101   $83.11   $83.10   $83.10  
  7 purchase totals = $819.38       $908.6369   $908.63   $908.65   $908.50