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 $16.46   5.273%   $17.3279   $17.33   $17.35   $17.30  
  Purchase #2 $164.84   10.692%   $182.4647   $182.46   $182.45   $182.50  
  Purchase #3 $157.26   11.197%   $174.8684   $174.87   $174.85   $174.90  
  Purchase #4 $192.99   6.740%   $205.9975   $206.00   $206.00   $206.00  
  Purchase #5 $224.55   3.679%   $232.8112   $232.81   $232.80   $232.80  
  Purchase #6 $59.96   4.749%   $62.8075   $62.81   $62.80   $62.80  
  Purchase #7 $30.90   13.456%   $35.0579   $35.06   $35.05   $35.10  
  7 purchase totals = $846.96       $911.3351   $911.34   $911.30   $911.40