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 $23.97   11.618%   $26.7548   $26.75   $26.75   $26.80  
  Purchase #2 $158.30   5.190%   $166.5158   $166.52   $166.50   $166.50  
  Purchase #3 $208.66   3.210%   $215.358   $215.36   $215.35   $215.40  
  Purchase #4 $174.47   7.327%   $187.2534   $187.25   $187.25   $187.30  
  Purchase #5 $193.72   9.677%   $212.4663   $212.47   $212.45   $212.50  
  Purchase #6 $119.52   10.863%   $132.5035   $132.50   $132.50   $132.50  
  Purchase #7 $58.99   4.862%   $61.8581   $61.86   $61.85   $61.90  
  7 purchase totals = $937.63       $1,002.7099   $1,002.71   $1,002.65   $1,002.90