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 $238.95   11.573%   $266.6037   $266.60   $266.60   $266.60  
  Purchase #2 $239.62   10.495%   $264.7681   $264.77   $264.75   $264.80  
  Purchase #3 $226.76   5.163%   $238.4676   $238.47   $238.45   $238.50  
  Purchase #4 $157.28   8.365%   $170.4365   $170.44   $170.45   $170.40  
  Purchase #5 $249.62   13.340%   $282.9193   $282.92   $282.90   $282.90  
  Purchase #6 $54.93   3.738%   $56.9833   $56.98   $57.00   $57.00  
  Purchase #7 $240.56   10.826%   $266.603   $266.60   $266.60   $266.60  
  7 purchase totals = $1,407.72       $1,546.7815   $1,546.78   $1,546.75   $1,546.80