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 $169.95   8.806%   $184.9158   $184.92   $184.90   $184.90  
  Purchase #2 $148.46   8.428%   $160.9722   $160.97   $160.95   $161.00  
  Purchase #3 $234.60   4.839%   $245.9523   $245.95   $245.95   $246.00  
  Purchase #4 $94.79   5.266%   $99.7816   $99.78   $99.80   $99.80  
  Purchase #5 $87.49   6.758%   $93.4026   $93.40   $93.40   $93.40  
  Purchase #6 $219.81   11.121%   $244.2551   $244.26   $244.25   $244.30  
  Purchase #7 $203.62   5.811%   $215.4524   $215.45   $215.45   $215.50  
  7 purchase totals = $1,158.72       $1,244.7320   $1,244.73   $1,244.70   $1,244.90