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 $62.80   9.603%   $68.8307   $68.83   $68.85   $68.80  
  Purchase #2 $117.74   7.781%   $126.9013   $126.90   $126.90   $126.90  
  Purchase #3 $218.85   9.207%   $238.9995   $239.00   $239.00   $239.00  
  Purchase #4 $61.28   5.603%   $64.7135   $64.71   $64.70   $64.70  
  Purchase #5 $7.92   8.820%   $8.6185   $8.62   $8.60   $8.60  
  Purchase #6 $164.70   12.167%   $184.739   $184.74   $184.75   $184.70  
  Purchase #7 $88.50   6.348%   $94.118   $94.12   $94.10   $94.10  
  7 purchase totals = $721.79       $786.9205   $786.92   $786.90   $786.80