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 $39.95   12.545%   $44.9617   $44.96   $44.95   $45.00  
  Purchase #2 $131.42   11.505%   $146.5399   $146.54   $146.55   $146.50  
  Purchase #3 $161.60   11.271%   $179.8139   $179.81   $179.80   $179.80  
  Purchase #4 $147.88   6.732%   $157.8353   $157.84   $157.85   $157.80  
  Purchase #5 $22.34   4.528%   $23.3516   $23.35   $23.35   $23.40  
  Purchase #6 $219.93   13.377%   $249.35   $249.35   $249.35   $249.40  
  Purchase #7 $150.70   6.376%   $160.3086   $160.31   $160.30   $160.30  
  7 purchase totals = $873.82       $962.1610   $962.16   $962.15   $962.20