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 $180.38   13.785%   $205.2454   $205.25   $205.25   $205.20  
  Purchase #2 $177.78   8.858%   $193.5278   $193.53   $193.55   $193.50  
  Purchase #3 $209.84   5.612%   $221.6162   $221.62   $221.60   $221.60  
  Purchase #4 $26.89   8.598%   $29.202   $29.20   $29.20   $29.20  
  Purchase #5 $24.45   3.633%   $25.3383   $25.34   $25.35   $25.30  
  Purchase #6 $244.37   4.165%   $254.548   $254.55   $254.55   $254.50  
  Purchase #7 $213.29   5.504%   $225.0295   $225.03   $225.05   $225.00  
  7 purchase totals = $1,077.00       $1,154.5072   $1,154.52   $1,154.55   $1,154.30