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 $96.93   9.710%   $106.3419   $106.34   $106.35   $106.30  
  Purchase #2 $247.88   7.270%   $265.9009   $265.90   $265.90   $265.90  
  Purchase #3 $21.63   9.146%   $23.6083   $23.61   $23.60   $23.60  
  Purchase #4 $123.35   7.794%   $132.9639   $132.96   $132.95   $133.00  
  Purchase #5 $110.59   7.786%   $119.2005   $119.20   $119.20   $119.20  
  Purchase #6 $124.74   13.343%   $141.3841   $141.38   $141.40   $141.40  
  Purchase #7 $78.51   3.794%   $81.4887   $81.49   $81.50   $81.50  
  7 purchase totals = $803.63       $870.8883   $870.88   $870.90   $870.90