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 $237.81   11.633%   $265.4744   $265.47   $265.45   $265.50  
  Purchase #2 $178.79   12.548%   $201.2246   $201.22   $201.20   $201.20  
  Purchase #3 $190.68   12.240%   $214.0192   $214.02   $214.00   $214.00  
  Purchase #4 $184.65   10.200%   $203.4843   $203.48   $203.50   $203.50  
  Purchase #5 $57.83   12.427%   $65.0165   $65.02   $65.00   $65.00  
  Purchase #6 $153.87   12.568%   $173.2084   $173.21   $173.20   $173.20  
  Purchase #7 $68.36   8.452%   $74.1378   $74.14   $74.15   $74.10  
  7 purchase totals = $1,071.99       $1,196.5652   $1,196.56   $1,196.50   $1,196.50