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 $60.84   9.802%   $66.8035   $66.80   $66.80   $66.80  
  Purchase #2 $119.84   6.414%   $127.5265   $127.53   $127.55   $127.50  
  Purchase #3 $206.72   3.641%   $214.2467   $214.25   $214.25   $214.20  
  Purchase #4 $232.38   13.302%   $263.2912   $263.29   $263.30   $263.30  
  Purchase #5 $156.99   9.726%   $172.2588   $172.26   $172.25   $172.30  
  Purchase #6 $228.26   13.159%   $258.2967   $258.30   $258.30   $258.30  
  Purchase #7 $84.85   8.826%   $92.3389   $92.34   $92.35   $92.30  
  7 purchase totals = $1,089.88       $1,194.7623   $1,194.77   $1,194.80   $1,194.70