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 $24.97   7.851%   $26.9304   $26.93   $26.95   $26.90  
  Purchase #2 $108.32   10.564%   $119.7629   $119.76   $119.75   $119.80  
  Purchase #3 $192.48   3.733%   $199.6653   $199.67   $199.65   $199.70  
  Purchase #4 $209.63   9.303%   $229.1319   $229.13   $229.15   $229.10  
  Purchase #5 $9.62   6.280%   $10.2241   $10.22   $10.20   $10.20  
  Purchase #6 $46.86   5.677%   $49.5202   $49.52   $49.50   $49.50  
  Purchase #7 $234.30   13.561%   $266.0734   $266.07   $266.05   $266.10  
  7 purchase totals = $826.18       $901.3082   $901.30   $901.25   $901.30