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 $238.70   10.578%   $263.9497   $263.95   $263.95   $263.90  
  Purchase #2 $98.36   12.559%   $110.713   $110.71   $110.70   $110.70  
  Purchase #3 $134.97   5.572%   $142.4905   $142.49   $142.50   $142.50  
  Purchase #4 $98.53   6.716%   $105.1473   $105.15   $105.15   $105.10  
  Purchase #5 $105.99   12.854%   $119.614   $119.61   $119.60   $119.60  
  Purchase #6 $30.90   6.713%   $32.9743   $32.97   $32.95   $33.00  
  Purchase #7 $34.45   7.658%   $37.0882   $37.09   $37.10   $37.10  
  7 purchase totals = $741.90       $811.9770   $811.97   $811.95   $811.90