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 $235.72   13.386%   $267.2735   $267.27   $267.25   $267.30  
  Purchase #2 $192.63   5.130%   $202.5119   $202.51   $202.50   $202.50  
  Purchase #3 $236.63   4.305%   $246.8169   $246.82   $246.80   $246.80  
  Purchase #4 $151.70   12.120%   $170.086   $170.09   $170.10   $170.10  
  Purchase #5 $47.96   4.633%   $50.182   $50.18   $50.20   $50.20  
  Purchase #6 $26.35   8.228%   $28.5181   $28.52   $28.50   $28.50  
  Purchase #7 $155.90   12.120%   $174.7951   $174.80   $174.80   $174.80  
  7 purchase totals = $1,046.89       $1,140.1835   $1,140.19   $1,140.15   $1,140.20