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 $86.87   12.325%   $97.5767   $97.58   $97.60   $97.60  
  Purchase #2 $236.89   11.863%   $264.9923   $264.99   $265.00   $265.00  
  Purchase #3 $61.32   7.221%   $65.7479   $65.75   $65.75   $65.70  
  Purchase #4 $9.58   4.596%   $10.0203   $10.02   $10.00   $10.00  
  Purchase #5 $149.57   7.545%   $160.8551   $160.86   $160.85   $160.90  
  Purchase #6 $73.59   8.206%   $79.6288   $79.63   $79.65   $79.60  
  Purchase #7 $231.70   7.831%   $249.8444   $249.84   $249.85   $249.80  
  7 purchase totals = $849.52       $928.6655   $928.67   $928.70   $928.60