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 $217.58   11.842%   $243.3458   $243.35   $243.35   $243.30  
  Purchase #2 $76.35   7.672%   $82.2076   $82.21   $82.20   $82.20  
  Purchase #3 $210.46   3.733%   $218.3165   $218.32   $218.30   $218.30  
  Purchase #4 $140.95   13.136%   $159.4652   $159.47   $159.45   $159.50  
  Purchase #5 $211.36   8.646%   $229.6342   $229.63   $229.65   $229.60  
  Purchase #6 $173.80   4.874%   $182.271   $182.27   $182.25   $182.30  
  Purchase #7 $130.83   6.422%   $139.2319   $139.23   $139.25   $139.20  
  7 purchase totals = $1,161.33       $1,254.4722   $1,254.48   $1,254.45   $1,254.40