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 $96.27   10.608%   $106.4823   $106.48   $106.50   $106.50  
  Purchase #2 $227.96   13.547%   $258.8417   $258.84   $258.85   $258.80  
  Purchase #3 $59.84   4.214%   $62.3617   $62.36   $62.35   $62.40  
  Purchase #4 $9.90   3.209%   $10.2177   $10.22   $10.20   $10.20  
  Purchase #5 $167.43   10.621%   $185.2127   $185.21   $185.20   $185.20  
  Purchase #6 $174.94   10.169%   $192.7296   $192.73   $192.75   $192.70  
  Purchase #7 $14.74   3.769%   $15.2956   $15.30   $15.30   $15.30  
  7 purchase totals = $751.08       $831.1413   $831.14   $831.15   $831.10