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 $59.58   6.402%   $63.3943   $63.39   $63.40   $63.40  
  Purchase #2 $198.49   11.781%   $221.8741   $221.87   $221.85   $221.90  
  Purchase #3 $107.37   6.734%   $114.6003   $114.60   $114.60   $114.60  
  Purchase #4 $30.61   13.776%   $34.8268   $34.83   $34.85   $34.80  
  Purchase #5 $67.87   10.146%   $74.7561   $74.76   $74.75   $74.80  
  Purchase #6 $190.96   11.869%   $213.625   $213.63   $213.65   $213.60  
  Purchase #7 $70.55   12.498%   $79.3673   $79.37   $79.35   $79.40  
  7 purchase totals = $725.43       $802.4439   $802.45   $802.45   $802.50