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 $86.77   7.517%   $93.2925   $93.29   $93.30   $93.30  
  Purchase #2 $174.69   11.791%   $195.2877   $195.29   $195.30   $195.30  
  Purchase #3 $127.32   11.552%   $142.028   $142.03   $142.05   $142.00  
  Purchase #4 $225.94   3.736%   $234.3811   $234.38   $234.40   $234.40  
  Purchase #5 $185.53   7.868%   $200.1275   $200.13   $200.15   $200.10  
  Purchase #6 $57.54   6.330%   $61.1823   $61.18   $61.20   $61.20  
  Purchase #7 $53.70   9.173%   $58.6259   $58.63   $58.65   $58.60  
  7 purchase totals = $911.49       $984.9250   $984.93   $985.05   $984.90