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 $68.61   8.531%   $74.4631   $74.46   $74.45   $74.50  
  Purchase #2 $70.63   6.221%   $75.0239   $75.02   $75.00   $75.00  
  Purchase #3 $250.98   7.225%   $269.1133   $269.11   $269.10   $269.10  
  Purchase #4 $233.60   11.102%   $259.5343   $259.53   $259.55   $259.50  
  Purchase #5 $64.43   5.461%   $67.9485   $67.95   $67.95   $67.90  
  Purchase #6 $35.89   11.699%   $40.0888   $40.09   $40.10   $40.10  
  Purchase #7 $185.75   7.810%   $200.2571   $200.26   $200.25   $200.30  
  7 purchase totals = $909.89       $986.4290   $986.42   $986.40   $986.40