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 $242.62   9.615%   $265.9479   $265.95   $265.95   $265.90  
  Purchase #2 $100.98   13.465%   $114.577   $114.58   $114.60   $114.60  
  Purchase #3 $225.94   8.310%   $244.7156   $244.72   $244.70   $244.70  
  Purchase #4 $92.80   11.716%   $103.6724   $103.67   $103.65   $103.70  
  Purchase #5 $49.52   6.225%   $52.6026   $52.60   $52.60   $52.60  
  Purchase #6 $195.73   10.325%   $215.9391   $215.94   $215.95   $215.90  
  Purchase #7 $53.89   8.537%   $58.4906   $58.49   $58.50   $58.50  
  7 purchase totals = $961.48       $1,055.9452   $1,055.95   $1,055.95   $1,055.90