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 $64.87   6.108%   $68.8323   $68.83   $68.85   $68.80  
  Purchase #2 $216.63   13.724%   $246.3603   $246.36   $246.35   $246.40  
  Purchase #3 $140.80   7.446%   $151.284   $151.28   $151.30   $151.30  
  Purchase #4 $150.89   4.754%   $158.0633   $158.06   $158.05   $158.10  
  Purchase #5 $14.96   3.141%   $15.4299   $15.43   $15.45   $15.40  
  Purchase #6 $24.96   8.264%   $27.0227   $27.02   $27.00   $27.00  
  Purchase #7 $86.87   13.194%   $98.3316   $98.33   $98.35   $98.30  
  7 purchase totals = $699.98       $765.3241   $765.31   $765.35   $765.30