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 $207.41   9.317%   $226.7344   $226.73   $226.75   $226.70  
  Purchase #2 $157.57   6.587%   $167.9491   $167.95   $167.95   $167.90  
  Purchase #3 $11.60   9.585%   $12.7119   $12.71   $12.70   $12.70  
  Purchase #4 $112.93   10.380%   $124.6521   $124.65   $124.65   $124.70  
  Purchase #5 $99.34   11.854%   $111.1158   $111.12   $111.10   $111.10  
  Purchase #6 $109.92   8.611%   $119.3852   $119.39   $119.40   $119.40  
  Purchase #7 $90.84   6.860%   $97.0716   $97.07   $97.05   $97.10  
  7 purchase totals = $789.61       $859.6201   $859.62   $859.60   $859.60