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 $206.88   13.273%   $234.3392   $234.34   $234.35   $234.30  
  Purchase #2 $96.31   8.485%   $104.4819   $104.48   $104.50   $104.50  
  Purchase #3 $39.75   10.864%   $44.0684   $44.07   $44.05   $44.10  
  Purchase #4 $246.83   9.449%   $270.153   $270.15   $270.15   $270.20  
  Purchase #5 $9.45   3.382%   $9.7696   $9.77   $9.75   $9.80  
  Purchase #6 $20.88   11.778%   $23.3392   $23.34   $23.35   $23.30  
  Purchase #7 $99.96   4.526%   $104.4842   $104.48   $104.50   $104.50  
  7 purchase totals = $720.06       $790.6355   $790.63   $790.65   $790.70