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 $57.59   5.369%   $60.682   $60.68   $60.70   $60.70  
  Purchase #2 $221.99   11.458%   $247.4256   $247.43   $247.45   $247.40  
  Purchase #3 $6.37   13.251%   $7.2141   $7.21   $7.20   $7.20  
  Purchase #4 $178.82   11.434%   $199.2663   $199.27   $199.25   $199.30  
  Purchase #5 $97.70   7.442%   $104.9708   $104.97   $104.95   $105.00  
  Purchase #6 $48.90   10.758%   $54.1607   $54.16   $54.15   $54.20  
  Purchase #7 $250.48   8.232%   $271.0995   $271.10   $271.10   $271.10  
  7 purchase totals = $861.85       $944.8190   $944.82   $944.80   $944.90