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 $168.49   9.554%   $184.5875   $184.59   $184.60   $184.60  
  Purchase #2 $35.44   10.873%   $39.2934   $39.29   $39.30   $39.30  
  Purchase #3 $81.81   13.539%   $92.8863   $92.89   $92.90   $92.90  
  Purchase #4 $230.73   9.170%   $251.8879   $251.89   $251.90   $251.90  
  Purchase #5 $103.86   10.378%   $114.6386   $114.64   $114.65   $114.60  
  Purchase #6 $151.42   3.618%   $156.8984   $156.90   $156.90   $156.90  
  Purchase #7 $173.99   11.791%   $194.5052   $194.51   $194.50   $194.50  
  7 purchase totals = $945.74       $1,034.6973   $1,034.71   $1,034.75   $1,034.70