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 $60.59   12.342%   $68.068   $68.07   $68.05   $68.10  
  Purchase #2 $117.86   6.657%   $125.7059   $125.71   $125.70   $125.70  
  Purchase #3 $71.49   8.103%   $77.2828   $77.28   $77.30   $77.30  
  Purchase #4 $192.78   4.355%   $201.1756   $201.18   $201.20   $201.20  
  Purchase #5 $130.81   3.332%   $135.1686   $135.17   $135.15   $135.20  
  Purchase #6 $153.59   10.138%   $169.161   $169.16   $169.15   $169.20  
  Purchase #7 $114.41   10.122%   $125.9906   $125.99   $126.00   $126.00  
  7 purchase totals = $841.53       $902.5525   $902.56   $902.55   $902.70