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 $64.35   5.321%   $67.7741   $67.77   $67.75   $67.80  
  Purchase #2 $193.34   3.292%   $199.7048   $199.70   $199.70   $199.70  
  Purchase #3 $84.55   3.626%   $87.6158   $87.62   $87.60   $87.60  
  Purchase #4 $64.84   9.566%   $71.0426   $71.04   $71.05   $71.00  
  Purchase #5 $45.97   10.226%   $50.6709   $50.67   $50.65   $50.70  
  Purchase #6 $92.46   9.552%   $101.2918   $101.29   $101.30   $101.30  
  Purchase #7 $119.53   5.826%   $126.4938   $126.49   $126.50   $126.50  
  7 purchase totals = $665.04       $704.5938   $704.58   $704.55   $704.60