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 $71.67   6.525%   $76.3465   $76.35   $76.35   $76.30  
  Purchase #2 $44.44   4.251%   $46.3291   $46.33   $46.35   $46.30  
  Purchase #3 $75.71   3.531%   $78.3833   $78.38   $78.40   $78.40  
  Purchase #4 $235.46   10.311%   $259.7383   $259.74   $259.75   $259.70  
  Purchase #5 $169.82   11.476%   $189.3085   $189.31   $189.30   $189.30  
  Purchase #6 $234.74   13.329%   $266.0285   $266.03   $266.05   $266.00  
  Purchase #7 $127.54   9.746%   $139.97   $139.97   $139.95   $140.00  
  7 purchase totals = $959.38       $1,056.1042   $1,056.11   $1,056.15   $1,056.00