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 $194.57   11.701%   $217.3366   $217.34   $217.35   $217.30  
  Purchase #2 $214.90   11.421%   $239.4437   $239.44   $239.45   $239.40  
  Purchase #3 $204.86   5.774%   $216.6886   $216.69   $216.70   $216.70  
  Purchase #4 $77.73   11.667%   $86.7988   $86.80   $86.80   $86.80  
  Purchase #5 $25.47   5.580%   $26.8912   $26.89   $26.90   $26.90  
  Purchase #6 $176.92   13.253%   $200.3672   $200.37   $200.35   $200.40  
  Purchase #7 $200.78   6.519%   $213.8688   $213.87   $213.85   $213.90  
  7 purchase totals = $1,095.23       $1,201.3949   $1,201.40   $1,201.40   $1,201.40