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 $65.63   3.381%   $67.849   $67.85   $67.85   $67.80  
  Purchase #2 $218.47   8.789%   $237.6713   $237.67   $237.65   $237.70  
  Purchase #3 $116.98   12.872%   $132.0377   $132.04   $132.05   $132.00  
  Purchase #4 $144.47   11.779%   $161.4871   $161.49   $161.50   $161.50  
  Purchase #5 $68.84   3.385%   $71.1702   $71.17   $71.15   $71.20  
  Purchase #6 $242.63   9.575%   $265.8618   $265.86   $265.85   $265.90  
  Purchase #7 $49.79   4.789%   $52.1744   $52.17   $52.15   $52.20  
  7 purchase totals = $906.81       $988.2515   $988.25   $988.20   $988.30