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 $84.95   10.179%   $93.5971   $93.60   $93.60   $93.60  
  Purchase #2 $51.68   4.403%   $53.9555   $53.96   $53.95   $54.00  
  Purchase #3 $125.53   6.770%   $134.0284   $134.03   $134.05   $134.00  
  Purchase #4 $208.85   5.653%   $220.6563   $220.66   $220.65   $220.70  
  Purchase #5 $31.43   4.637%   $32.8874   $32.89   $32.90   $32.90  
  Purchase #6 $55.60   5.704%   $58.7714   $58.77   $58.75   $58.80  
  Purchase #7 $117.35   6.685%   $125.1948   $125.19   $125.20   $125.20  
  7 purchase totals = $675.39       $719.0909   $719.10   $719.10   $719.20