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 $54.32   10.827%   $60.2012   $60.20   $60.20   $60.20  
  Purchase #2 $185.68   10.634%   $205.4252   $205.43   $205.45   $205.40  
  Purchase #3 $138.91   8.844%   $151.1952   $151.20   $151.20   $151.20  
  Purchase #4 $196.81   11.550%   $219.5416   $219.54   $219.55   $219.50  
  Purchase #5 $131.63   9.351%   $143.9387   $143.94   $143.95   $143.90  
  Purchase #6 $111.49   13.464%   $126.501   $126.50   $126.50   $126.50  
  Purchase #7 $51.36   3.692%   $53.2562   $53.26   $53.25   $53.30  
  7 purchase totals = $870.20       $960.0591   $960.07   $960.10   $960.00