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 $65.61   4.509%   $68.5684   $68.57   $68.55   $68.60  
  Purchase #2 $117.98   7.210%   $126.4864   $126.49   $126.50   $126.50  
  Purchase #3 $110.99   11.591%   $123.8549   $123.85   $123.85   $123.90  
  Purchase #4 $50.43   7.675%   $54.3005   $54.30   $54.30   $54.30  
  Purchase #5 $217.72   13.683%   $247.5106   $247.51   $247.50   $247.50  
  Purchase #6 $108.84   12.337%   $122.2676   $122.27   $122.25   $122.30  
  Purchase #7 $174.79   4.269%   $182.2518   $182.25   $182.25   $182.30  
  7 purchase totals = $846.36       $925.2402   $925.24   $925.20   $925.40