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 $99.35   3.466%   $102.7935   $102.79   $102.80   $102.80  
  Purchase #2 $28.81   7.192%   $30.882   $30.88   $30.90   $30.90  
  Purchase #3 $192.25   4.665%   $201.2185   $201.22   $201.20   $201.20  
  Purchase #4 $172.66   8.198%   $186.8147   $186.81   $186.80   $186.80  
  Purchase #5 $241.27   9.388%   $263.9204   $263.92   $263.90   $263.90  
  Purchase #6 $18.47   12.205%   $20.7243   $20.72   $20.70   $20.70  
  Purchase #7 $28.47   4.153%   $29.6524   $29.65   $29.65   $29.70  
  7 purchase totals = $781.28       $836.0058   $835.99   $835.95   $836.00