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 $63.88   7.236%   $68.5024   $68.50   $68.50   $68.50  
  Purchase #2 $231.67   8.851%   $252.1751   $252.18   $252.20   $252.20  
  Purchase #3 $14.81   10.208%   $16.3218   $16.32   $16.30   $16.30  
  Purchase #4 $194.39   3.299%   $200.8029   $200.80   $200.80   $200.80  
  Purchase #5 $155.94   3.462%   $161.3386   $161.34   $161.35   $161.30  
  Purchase #6 $197.26   12.735%   $222.3811   $222.38   $222.40   $222.40  
  Purchase #7 $70.46   6.456%   $75.0089   $75.01   $75.00   $75.00  
  7 purchase totals = $928.41       $996.5308   $996.53   $996.55   $996.50