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 $88.46   11.461%   $98.5984   $98.60   $98.60   $98.60  
  Purchase #2 $108.98   6.313%   $115.8599   $115.86   $115.85   $115.90  
  Purchase #3 $40.99   4.872%   $42.987   $42.99   $43.00   $43.00  
  Purchase #4 $179.72   11.681%   $200.7131   $200.71   $200.70   $200.70  
  Purchase #5 $90.84   5.112%   $95.4837   $95.48   $95.50   $95.50  
  Purchase #6 $249.88   11.735%   $279.2034   $279.20   $279.20   $279.20  
  Purchase #7 $208.26   3.589%   $215.7345   $215.73   $215.75   $215.70  
  7 purchase totals = $967.13       $1,048.5800   $1,048.57   $1,048.60   $1,048.60