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 $210.34   12.248%   $236.1024   $236.10   $236.10   $236.10  
  Purchase #2 $157.51   12.361%   $176.9798   $176.98   $177.00   $177.00  
  Purchase #3 $73.42   12.804%   $82.8207   $82.82   $82.80   $82.80  
  Purchase #4 $146.96   4.508%   $153.585   $153.59   $153.60   $153.60  
  Purchase #5 $183.99   12.477%   $206.9464   $206.95   $206.95   $206.90  
  Purchase #6 $31.62   10.294%   $34.875   $34.88   $34.90   $34.90  
  Purchase #7 $208.46   6.475%   $221.9578   $221.96   $221.95   $222.00  
  7 purchase totals = $1,012.30       $1,113.2671   $1,113.28   $1,113.30   $1,113.30