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 $91.29   5.838%   $96.6195   $96.62   $96.60   $96.60  
  Purchase #2 $89.25   6.308%   $94.8799   $94.88   $94.90   $94.90  
  Purchase #3 $237.36   5.816%   $251.1649   $251.16   $251.15   $251.20  
  Purchase #4 $146.88   10.116%   $161.7384   $161.74   $161.75   $161.70  
  Purchase #5 $82.65   9.261%   $90.3042   $90.30   $90.30   $90.30  
  Purchase #6 $48.75   10.553%   $53.8946   $53.89   $53.90   $53.90  
  Purchase #7 $197.51   7.168%   $211.6675   $211.67   $211.65   $211.70  
  7 purchase totals = $893.69       $960.2690   $960.26   $960.25   $960.30