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 $44.54   9.862%   $48.9325   $48.93   $48.95   $48.90  
  Purchase #2 $111.55   12.596%   $125.6008   $125.60   $125.60   $125.60  
  Purchase #3 $247.76   12.155%   $277.8752   $277.88   $277.90   $277.90  
  Purchase #4 $177.30   10.684%   $196.2427   $196.24   $196.25   $196.20  
  Purchase #5 $41.46   11.756%   $46.334   $46.33   $46.35   $46.30  
  Purchase #6 $76.44   11.158%   $84.9692   $84.97   $84.95   $85.00  
  Purchase #7 $250.42   3.379%   $258.8817   $258.88   $258.90   $258.90  
  7 purchase totals = $949.47       $1,038.8361   $1,038.83   $1,038.90   $1,038.80