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 $60.76   6.490%   $64.7033   $64.70   $64.70   $64.70  
  Purchase #2 $144.95   8.713%   $157.5795   $157.58   $157.60   $157.60  
  Purchase #3 $185.48   12.309%   $208.3107   $208.31   $208.30   $208.30  
  Purchase #4 $55.55   13.254%   $62.9126   $62.91   $62.90   $62.90  
  Purchase #5 $45.77   10.295%   $50.482   $50.48   $50.50   $50.50  
  Purchase #6 $24.43   7.837%   $26.3446   $26.34   $26.35   $26.30  
  Purchase #7 $248.78   10.582%   $275.1059   $275.11   $275.10   $275.10  
  7 purchase totals = $765.72       $845.4386   $845.43   $845.45   $845.40