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 $61.95   6.246%   $65.8194   $65.82   $65.80   $65.80  
  Purchase #2 $247.73   13.841%   $282.0183   $282.02   $282.00   $282.00  
  Purchase #3 $55.36   9.856%   $60.8163   $60.82   $60.80   $60.80  
  Purchase #4 $201.37   8.387%   $218.2589   $218.26   $218.25   $218.30  
  Purchase #5 $104.30   8.171%   $112.8224   $112.82   $112.80   $112.80  
  Purchase #6 $226.44   11.431%   $252.3244   $252.32   $252.30   $252.30  
  Purchase #7 $55.60   6.472%   $59.1984   $59.20   $59.20   $59.20  
  7 purchase totals = $952.75       $1,051.2581   $1,051.26   $1,051.15   $1,051.20