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 $203.26   4.804%   $213.0246   $213.02   $213.00   $213.00  
  Purchase #2 $215.64   10.758%   $238.8386   $238.84   $238.85   $238.80  
  Purchase #3 $68.59   12.221%   $76.9724   $76.97   $76.95   $77.00  
  Purchase #4 $114.69   10.630%   $126.8815   $126.88   $126.90   $126.90  
  Purchase #5 $233.63   12.381%   $262.5557   $262.56   $262.55   $262.60  
  Purchase #6 $162.57   13.624%   $184.7185   $184.72   $184.70   $184.70  
  Purchase #7 $223.96   9.346%   $244.8913   $244.89   $244.90   $244.90  
  7 purchase totals = $1,222.34       $1,347.8826   $1,347.88   $1,347.85   $1,347.90