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 $67.39   11.765%   $75.3184   $75.32   $75.30   $75.30  
  Purchase #2 $72.63   11.118%   $80.705   $80.71   $80.70   $80.70  
  Purchase #3 $182.32   5.405%   $192.1744   $192.17   $192.15   $192.20  
  Purchase #4 $44.50   8.327%   $48.2055   $48.21   $48.20   $48.20  
  Purchase #5 $103.43   9.518%   $113.2745   $113.27   $113.25   $113.30  
  Purchase #6 $186.81   6.844%   $199.5953   $199.60   $199.60   $199.60  
  Purchase #7 $48.45   5.162%   $50.951   $50.95   $50.95   $51.00  
  7 purchase totals = $705.53       $760.2241   $760.23   $760.15   $760.30