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 $250.56   6.228%   $266.1649   $266.16   $266.15   $266.20  
  Purchase #2 $185.90   8.579%   $201.8484   $201.85   $201.85   $201.80  
  Purchase #3 $83.26   4.784%   $87.2432   $87.24   $87.25   $87.20  
  Purchase #4 $52.39   4.490%   $54.7423   $54.74   $54.75   $54.70  
  Purchase #5 $181.46   8.838%   $197.4974   $197.50   $197.50   $197.50  
  Purchase #6 $217.70   12.778%   $245.5177   $245.52   $245.50   $245.50  
  Purchase #7 $159.25   3.188%   $164.3269   $164.33   $164.35   $164.30  
  7 purchase totals = $1,130.52       $1,217.3408   $1,217.34   $1,217.35   $1,217.20