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 $234.36   11.503%   $261.3184   $261.32   $261.30   $261.30  
  Purchase #2 $201.86   4.183%   $210.3038   $210.30   $210.30   $210.30  
  Purchase #3 $39.73   12.298%   $44.616   $44.62   $44.60   $44.60  
  Purchase #4 $150.72   10.423%   $166.4295   $166.43   $166.45   $166.40  
  Purchase #5 $146.93   3.114%   $151.5054   $151.51   $151.50   $151.50  
  Purchase #6 $199.26   3.255%   $205.7459   $205.75   $205.75   $205.70  
  Purchase #7 $38.54   9.677%   $42.2695   $42.27   $42.25   $42.30  
  7 purchase totals = $1,011.40       $1,082.1885   $1,082.20   $1,082.15   $1,082.10