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 $246.81   8.260%   $267.1965   $267.20   $267.20   $267.20  
  Purchase #2 $232.68   9.577%   $254.9638   $254.96   $254.95   $255.00  
  Purchase #3 $68.63   13.714%   $78.0419   $78.04   $78.05   $78.00  
  Purchase #4 $114.95   6.142%   $122.0102   $122.01   $122.00   $122.00  
  Purchase #5 $5.34   7.307%   $5.7302   $5.73   $5.75   $5.70  
  Purchase #6 $118.98   5.260%   $125.2383   $125.24   $125.25   $125.20  
  Purchase #7 $75.62   6.499%   $80.5345   $80.53   $80.55   $80.50  
  7 purchase totals = $863.01       $933.7154   $933.71   $933.75   $933.60