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 $56.67   6.657%   $60.4425   $60.44   $60.45   $60.40  
  Purchase #2 $200.86   6.668%   $214.2533   $214.25   $214.25   $214.30  
  Purchase #3 $211.30   10.338%   $233.1442   $233.14   $233.15   $233.10  
  Purchase #4 $166.37   12.852%   $187.7519   $187.75   $187.75   $187.80  
  Purchase #5 $162.86   3.204%   $168.078   $168.08   $168.10   $168.10  
  Purchase #6 $248.91   3.297%   $257.1166   $257.12   $257.10   $257.10  
  Purchase #7 $39.95   4.142%   $41.6047   $41.60   $41.60   $41.60  
  7 purchase totals = $1,086.92       $1,162.3912   $1,162.38   $1,162.40   $1,162.40