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 $195.33   3.763%   $202.6803   $202.68   $202.70   $202.70  
  Purchase #2 $242.91   13.743%   $276.2931   $276.29   $276.30   $276.30  
  Purchase #3 $199.96   7.322%   $214.6011   $214.60   $214.60   $214.60  
  Purchase #4 $53.54   12.849%   $60.4194   $60.42   $60.40   $60.40  
  Purchase #5 $196.27   12.103%   $220.0246   $220.02   $220.00   $220.00  
  Purchase #6 $151.33   13.698%   $172.0592   $172.06   $172.05   $172.10  
  Purchase #7 $112.68   8.641%   $122.4167   $122.42   $122.40   $122.40  
  7 purchase totals = $1,152.02       $1,268.4944   $1,268.49   $1,268.45   $1,268.50