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 $177.37   8.356%   $192.191   $192.19   $192.20   $192.20  
  Purchase #2 $56.29   7.231%   $60.3603   $60.36   $60.35   $60.40  
  Purchase #3 $139.43   11.649%   $155.6722   $155.67   $155.65   $155.70  
  Purchase #4 $108.81   3.724%   $112.8621   $112.86   $112.85   $112.90  
  Purchase #5 $16.56   4.265%   $17.2663   $17.27   $17.25   $17.30  
  Purchase #6 $35.56   11.312%   $39.5825   $39.58   $39.60   $39.60  
  Purchase #7 $152.85   13.752%   $173.8699   $173.87   $173.85   $173.90  
  7 purchase totals = $686.87       $751.8043   $751.80   $751.75   $752.00