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 $96.63   10.351%   $106.6322   $106.63   $106.65   $106.60  
  Purchase #2 $85.55   11.501%   $95.3891   $95.39   $95.40   $95.40  
  Purchase #3 $100.86   11.514%   $112.473   $112.47   $112.45   $112.50  
  Purchase #4 $185.84   10.672%   $205.6728   $205.67   $205.65   $205.70  
  Purchase #5 $132.59   3.151%   $136.7679   $136.77   $136.75   $136.80  
  Purchase #6 $234.80   5.138%   $246.864   $246.86   $246.85   $246.90  
  Purchase #7 $125.92   11.733%   $140.6942   $140.69   $140.70   $140.70  
  7 purchase totals = $962.19       $1,044.4932   $1,044.48   $1,044.45   $1,044.60