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 $239.89   12.211%   $269.183   $269.18   $269.20   $269.20  
  Purchase #2 $246.77   11.462%   $275.0548   $275.05   $275.05   $275.10  
  Purchase #3 $85.65   8.530%   $92.9559   $92.96   $92.95   $93.00  
  Purchase #4 $48.49   5.293%   $51.0566   $51.06   $51.05   $51.10  
  Purchase #5 $245.83   6.794%   $262.5317   $262.53   $262.55   $262.50  
  Purchase #6 $236.28   5.444%   $249.1431   $249.14   $249.15   $249.10  
  Purchase #7 $8.69   11.585%   $9.6967   $9.70   $9.70   $9.70  
  7 purchase totals = $1,111.60       $1,209.6218   $1,209.62   $1,209.65   $1,209.70