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 $186.80   4.173%   $194.5952   $194.60   $194.60   $194.60  
  Purchase #2 $188.58   13.440%   $213.9252   $213.93   $213.95   $213.90  
  Purchase #3 $246.63   3.479%   $255.2103   $255.21   $255.20   $255.20  
  Purchase #4 $182.49   3.199%   $188.3279   $188.33   $188.35   $188.30  
  Purchase #5 $121.70   9.235%   $132.939   $132.94   $132.95   $132.90  
  Purchase #6 $204.67   9.633%   $224.3859   $224.39   $224.40   $224.40  
  Purchase #7 $151.75   3.870%   $157.6227   $157.62   $157.60   $157.60  
  7 purchase totals = $1,282.62       $1,367.0062   $1,367.02   $1,367.05   $1,366.90