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 $23.65   9.403%   $25.8738   $25.87   $25.85   $25.90  
  Purchase #2 $162.77   7.423%   $174.8524   $174.85   $174.85   $174.90  
  Purchase #3 $155.35   5.141%   $163.3365   $163.34   $163.35   $163.30  
  Purchase #4 $163.51   7.687%   $176.079   $176.08   $176.10   $176.10  
  Purchase #5 $158.25   10.664%   $175.1258   $175.13   $175.15   $175.10  
  Purchase #6 $227.81   12.141%   $255.4684   $255.47   $255.45   $255.50  
  Purchase #7 $78.84   4.196%   $82.1481   $82.15   $82.15   $82.10  
  7 purchase totals = $970.18       $1,052.8840   $1,052.89   $1,052.90   $1,052.90