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 $62.67   8.716%   $68.1323   $68.13   $68.15   $68.10  
  Purchase #2 $32.75   3.828%   $34.0037   $34.00   $34.00   $34.00  
  Purchase #3 $187.95   12.750%   $211.9136   $211.91   $211.90   $211.90  
  Purchase #4 $153.27   12.614%   $172.6035   $172.60   $172.60   $172.60  
  Purchase #5 $153.43   3.811%   $159.2772   $159.28   $159.30   $159.30  
  Purchase #6 $168.40   8.806%   $183.2293   $183.23   $183.25   $183.20  
  Purchase #7 $216.37   9.144%   $236.1549   $236.15   $236.15   $236.20  
  7 purchase totals = $974.84       $1,065.3145   $1,065.30   $1,065.35   $1,065.30