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 $227.46   11.317%   $253.2016   $253.20   $253.20   $253.20  
  Purchase #2 $147.58   4.524%   $154.2565   $154.26   $154.25   $154.30  
  Purchase #3 $19.50   8.178%   $21.0947   $21.09   $21.10   $21.10  
  Purchase #4 $15.47   3.794%   $16.0569   $16.06   $16.05   $16.10  
  Purchase #5 $107.92   10.850%   $119.6293   $119.63   $119.65   $119.60  
  Purchase #6 $234.74   5.478%   $247.5991   $247.60   $247.60   $247.60  
  Purchase #7 $153.88   13.150%   $174.1152   $174.12   $174.10   $174.10  
  7 purchase totals = $906.55       $985.9533   $985.96   $985.95   $986.00