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 $78.94   11.587%   $88.0868   $88.09   $88.10   $88.10  
  Purchase #2 $55.86   3.689%   $57.9207   $57.92   $57.90   $57.90  
  Purchase #3 $55.37   13.781%   $63.0005   $63.00   $63.00   $63.00  
  Purchase #4 $109.30   4.848%   $114.5989   $114.60   $114.60   $114.60  
  Purchase #5 $199.44   3.333%   $206.0873   $206.09   $206.10   $206.10  
  Purchase #6 $224.99   11.714%   $251.3453   $251.35   $251.35   $251.30  
  Purchase #7 $236.64   5.549%   $249.7712   $249.77   $249.75   $249.80  
  7 purchase totals = $960.54       $1,030.8107   $1,030.82   $1,030.80   $1,030.80