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 $237.78   13.318%   $269.4475   $269.45   $269.45   $269.40  
  Purchase #2 $56.34   4.370%   $58.8021   $58.80   $58.80   $58.80  
  Purchase #3 $62.82   6.815%   $67.1012   $67.10   $67.10   $67.10  
  Purchase #4 $14.62   6.853%   $15.6219   $15.62   $15.60   $15.60  
  Purchase #5 $55.70   11.779%   $62.2609   $62.26   $62.25   $62.30  
  Purchase #6 $143.93   13.209%   $162.9417   $162.94   $162.95   $162.90  
  Purchase #7 $192.68   12.131%   $216.054   $216.05   $216.05   $216.10  
  7 purchase totals = $763.87       $852.2293   $852.22   $852.20   $852.20