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 $190.47   8.134%   $205.9628   $205.96   $205.95   $206.00  
  Purchase #2 $94.96   9.128%   $103.6279   $103.63   $103.65   $103.60  
  Purchase #3 $226.63   13.491%   $257.2047   $257.20   $257.20   $257.20  
  Purchase #4 $36.89   7.325%   $39.5922   $39.59   $39.60   $39.60  
  Purchase #5 $90.80   10.631%   $100.4529   $100.45   $100.45   $100.50  
  Purchase #6 $97.77   7.643%   $105.2426   $105.24   $105.25   $105.20  
  Purchase #7 $240.58   9.306%   $262.9684   $262.97   $262.95   $263.00  
  7 purchase totals = $978.10       $1,075.0515   $1,075.04   $1,075.05   $1,075.10