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 $191.44   11.795%   $214.0203   $214.02   $214.00   $214.00  
  Purchase #2 $106.98   6.244%   $113.6598   $113.66   $113.65   $113.70  
  Purchase #3 $53.54   11.371%   $59.628   $59.63   $59.65   $59.60  
  Purchase #4 $115.75   6.669%   $123.4694   $123.47   $123.45   $123.50  
  Purchase #5 $194.45   3.757%   $201.7555   $201.76   $201.75   $201.80  
  Purchase #6 $57.90   12.157%   $64.9389   $64.94   $64.95   $64.90  
  Purchase #7 $208.45   5.439%   $219.7876   $219.79   $219.80   $219.80  
  7 purchase totals = $928.51       $997.2595   $997.27   $997.25   $997.30