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 $107.46   7.254%   $115.2551   $115.26   $115.25   $115.30  
  Purchase #2 $83.70   9.375%   $91.5469   $91.55   $91.55   $91.50  
  Purchase #3 $89.78   5.774%   $94.9639   $94.96   $94.95   $95.00  
  Purchase #4 $163.51   11.491%   $182.2989   $182.30   $182.30   $182.30  
  Purchase #5 $222.53   4.192%   $231.8585   $231.86   $231.85   $231.90  
  Purchase #6 $117.90   5.567%   $124.4635   $124.46   $124.45   $124.50  
  Purchase #7 $162.32   7.164%   $173.9486   $173.95   $173.95   $173.90  
  7 purchase totals = $947.20       $1,014.3354   $1,014.34   $1,014.30   $1,014.40