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 $239.51   10.785%   $265.3412   $265.34   $265.35   $265.30  
  Purchase #2 $61.84   8.659%   $67.1947   $67.19   $67.20   $67.20  
  Purchase #3 $219.80   11.515%   $245.11   $245.11   $245.10   $245.10  
  Purchase #4 $98.59   13.792%   $112.1875   $112.19   $112.20   $112.20  
  Purchase #5 $62.41   10.556%   $68.998   $69.00   $69.00   $69.00  
  Purchase #6 $18.39   6.264%   $19.5419   $19.54   $19.55   $19.50  
  Purchase #7 $155.89   8.734%   $169.5054   $169.51   $169.50   $169.50  
  7 purchase totals = $856.43       $947.8787   $947.88   $947.90   $947.80