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 $217.39   11.279%   $241.9094   $241.91   $241.90   $241.90  
  Purchase #2 $225.39   7.572%   $242.4565   $242.46   $242.45   $242.50  
  Purchase #3 $150.63   5.466%   $158.8634   $158.86   $158.85   $158.90  
  Purchase #4 $22.64   4.375%   $23.6305   $23.63   $23.65   $23.60  
  Purchase #5 $27.86   4.794%   $29.1956   $29.20   $29.20   $29.20  
  Purchase #6 $99.31   4.725%   $104.0024   $104.00   $104.00   $104.00  
  Purchase #7 $68.48   4.207%   $71.361   $71.36   $71.35   $71.40  
  7 purchase totals = $811.70       $871.4188   $871.42   $871.40   $871.50