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 $140.71   9.558%   $154.1591   $154.16   $154.15   $154.20  
  Purchase #2 $85.59   13.163%   $96.8562   $96.86   $96.85   $96.90  
  Purchase #3 $114.33   4.544%   $119.5252   $119.53   $119.55   $119.50  
  Purchase #4 $58.62   4.433%   $61.2186   $61.22   $61.20   $61.20  
  Purchase #5 $16.88   12.337%   $18.9625   $18.96   $18.95   $19.00  
  Purchase #6 $241.63   5.232%   $254.2721   $254.27   $254.25   $254.30  
  Purchase #7 $103.53   12.239%   $116.201   $116.20   $116.20   $116.20  
  7 purchase totals = $761.29       $821.1947   $821.20   $821.15   $821.30