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 $44.57   11.462%   $49.6786   $49.68   $49.70   $49.70  
  Purchase #2 $75.96   12.115%   $85.1626   $85.16   $85.15   $85.20  
  Purchase #3 $139.49   6.714%   $148.8554   $148.86   $148.85   $148.90  
  Purchase #4 $50.94   11.670%   $56.8847   $56.88   $56.90   $56.90  
  Purchase #5 $208.31   4.583%   $217.8568   $217.86   $217.85   $217.90  
  Purchase #6 $226.87   10.845%   $251.4741   $251.47   $251.45   $251.50  
  Purchase #7 $80.50   9.803%   $88.3914   $88.39   $88.40   $88.40  
  7 purchase totals = $826.64       $898.3036   $898.30   $898.30   $898.50