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 $73.87   13.569%   $83.8934   $83.89   $83.90   $83.90  
  Purchase #2 $248.83   9.140%   $271.5731   $271.57   $271.55   $271.60  
  Purchase #3 $146.55   11.342%   $163.1717   $163.17   $163.15   $163.20  
  Purchase #4 $77.30   10.761%   $85.6183   $85.62   $85.60   $85.60  
  Purchase #5 $70.77   9.698%   $77.6333   $77.63   $77.65   $77.60  
  Purchase #6 $66.28   12.210%   $74.3728   $74.37   $74.35   $74.40  
  Purchase #7 $231.29   4.260%   $241.143   $241.14   $241.15   $241.10  
  7 purchase totals = $914.89       $997.4056   $997.39   $997.35   $997.40