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 $202.78   8.727%   $220.4766   $220.48   $220.50   $220.50  
  Purchase #2 $58.45   7.485%   $62.825   $62.83   $62.85   $62.80  
  Purchase #3 $69.36   5.487%   $73.1658   $73.17   $73.15   $73.20  
  Purchase #4 $9.93   7.367%   $10.6615   $10.66   $10.65   $10.70  
  Purchase #5 $189.51   4.872%   $198.7429   $198.74   $198.75   $198.70  
  Purchase #6 $88.27   4.508%   $92.2492   $92.25   $92.25   $92.20  
  Purchase #7 $206.73   13.352%   $234.3326   $234.33   $234.35   $234.30  
  7 purchase totals = $825.03       $892.4536   $892.46   $892.50   $892.40