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 $120.63   8.265%   $130.6001   $130.60   $130.60   $130.60  
  Purchase #2 $202.89   7.147%   $217.3905   $217.39   $217.40   $217.40  
  Purchase #3 $244.58   3.835%   $253.9596   $253.96   $253.95   $254.00  
  Purchase #4 $230.60   7.262%   $247.3462   $247.35   $247.35   $247.30  
  Purchase #5 $86.99   9.491%   $95.2462   $95.25   $95.25   $95.20  
  Purchase #6 $87.26   10.131%   $96.1003   $96.10   $96.10   $96.10  
  Purchase #7 $208.98   6.257%   $222.0559   $222.06   $222.05   $222.10  
  7 purchase totals = $1,181.93       $1,262.6988   $1,262.71   $1,262.70   $1,262.70