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 $217.46   10.104%   $239.4322   $239.43   $239.45   $239.40  
  Purchase #2 $242.36   8.282%   $262.4323   $262.43   $262.45   $262.40  
  Purchase #3 $97.97   8.491%   $106.2886   $106.29   $106.30   $106.30  
  Purchase #4 $96.25   12.103%   $107.8991   $107.90   $107.90   $107.90  
  Purchase #5 $243.39   12.298%   $273.3221   $273.32   $273.30   $273.30  
  Purchase #6 $84.58   8.247%   $91.5553   $91.56   $91.55   $91.60  
  Purchase #7 $243.80   12.168%   $273.4656   $273.47   $273.45   $273.50  
  7 purchase totals = $1,225.81       $1,354.3952   $1,354.40   $1,354.40   $1,354.40