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 $191.97   5.254%   $202.0561   $202.06   $202.05   $202.10  
  Purchase #2 $169.26   13.393%   $191.929   $191.93   $191.95   $191.90  
  Purchase #3 $150.29   11.105%   $166.9797   $166.98   $167.00   $167.00  
  Purchase #4 $112.87   6.255%   $119.93   $119.93   $119.95   $119.90  
  Purchase #5 $105.95   10.346%   $116.9116   $116.91   $116.90   $116.90  
  Purchase #6 $160.76   5.130%   $169.007   $169.01   $169.00   $169.00  
  Purchase #7 $13.44   10.692%   $14.877   $14.88   $14.90   $14.90  
  7 purchase totals = $904.54       $981.6904   $981.70   $981.75   $981.70