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 $244.98   9.449%   $268.1282   $268.13   $268.15   $268.10  
  Purchase #2 $197.50   6.462%   $210.2625   $210.26   $210.25   $210.30  
  Purchase #3 $70.53   6.543%   $75.1448   $75.14   $75.15   $75.10  
  Purchase #4 $237.79   9.157%   $259.5644   $259.56   $259.55   $259.60  
  Purchase #5 $194.95   3.494%   $201.7616   $201.76   $201.75   $201.80  
  Purchase #6 $144.92   11.855%   $162.1003   $162.10   $162.10   $162.10  
  Purchase #7 $142.62   3.783%   $148.0153   $148.02   $148.00   $148.00  
  7 purchase totals = $1,233.29       $1,324.9771   $1,324.97   $1,324.95   $1,325.00