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 $238.61   8.589%   $259.1042   $259.10   $259.10   $259.10  
  Purchase #2 $58.28   11.258%   $64.8412   $64.84   $64.85   $64.80  
  Purchase #3 $214.51   11.737%   $239.687   $239.69   $239.70   $239.70  
  Purchase #4 $244.95   3.132%   $252.6218   $252.62   $252.60   $252.60  
  Purchase #5 $42.78   5.634%   $45.1902   $45.19   $45.20   $45.20  
  Purchase #6 $238.40   4.679%   $249.5547   $249.55   $249.55   $249.60  
  Purchase #7 $245.35   4.667%   $256.8005   $256.80   $256.80   $256.80  
  7 purchase totals = $1,282.88       $1,367.7996   $1,367.79   $1,367.80   $1,367.80