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 $136.64   13.192%   $154.6655   $154.67   $154.65   $154.70  
  Purchase #2 $109.69   6.752%   $117.0963   $117.10   $117.10   $117.10  
  Purchase #3 $11.33   5.565%   $11.9605   $11.96   $11.95   $12.00  
  Purchase #4 $160.70   4.247%   $167.5249   $167.52   $167.50   $167.50  
  Purchase #5 $102.28   10.239%   $112.7524   $112.75   $112.75   $112.80  
  Purchase #6 $233.62   13.804%   $265.8689   $265.87   $265.85   $265.90  
  Purchase #7 $182.45   4.824%   $191.2514   $191.25   $191.25   $191.30  
  7 purchase totals = $936.71       $1,021.1199   $1,021.12   $1,021.05   $1,021.30