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 $208.41   5.450%   $219.7683   $219.77   $219.75   $219.80  
  Purchase #2 $241.96   4.527%   $252.9135   $252.91   $252.90   $252.90  
  Purchase #3 $78.34   5.533%   $82.6746   $82.67   $82.65   $82.70  
  Purchase #4 $98.86   5.871%   $104.6641   $104.66   $104.65   $104.70  
  Purchase #5 $96.95   12.231%   $108.808   $108.81   $108.80   $108.80  
  Purchase #6 $50.51   11.167%   $56.1505   $56.15   $56.15   $56.20  
  Purchase #7 $14.35   3.429%   $14.8421   $14.84   $14.85   $14.80  
  7 purchase totals = $789.38       $839.8211   $839.81   $839.75   $839.90