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 $58.44   3.865%   $60.6987   $60.70   $60.70   $60.70  
  Purchase #2 $31.90   6.853%   $34.0861   $34.09   $34.10   $34.10  
  Purchase #3 $231.70   5.859%   $245.2753   $245.28   $245.30   $245.30  
  Purchase #4 $127.42   8.221%   $137.8952   $137.90   $137.90   $137.90  
  Purchase #5 $35.83   13.315%   $40.6008   $40.60   $40.60   $40.60  
  Purchase #6 $139.84   9.326%   $152.8815   $152.88   $152.90   $152.90  
  Purchase #7 $31.63   9.344%   $34.5855   $34.59   $34.60   $34.60  
  7 purchase totals = $656.76       $706.0231   $706.04   $706.10   $706.10