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 $61.38   9.124%   $66.9803   $66.98   $67.00   $67.00  
  Purchase #2 $210.89   12.357%   $236.9497   $236.95   $236.95   $236.90  
  Purchase #3 $172.73   7.218%   $185.1977   $185.20   $185.20   $185.20  
  Purchase #4 $35.77   5.382%   $37.6951   $37.70   $37.70   $37.70  
  Purchase #5 $225.50   10.492%   $249.1595   $249.16   $249.15   $249.20  
  Purchase #6 $51.65   10.768%   $57.2117   $57.21   $57.20   $57.20  
  Purchase #7 $240.59   3.124%   $248.106   $248.11   $248.10   $248.10  
  7 purchase totals = $998.51       $1,081.3000   $1,081.31   $1,081.30   $1,081.30