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 $68.62   4.643%   $71.806   $71.81   $71.80   $71.80  
  Purchase #2 $242.58   8.347%   $262.8282   $262.83   $262.85   $262.80  
  Purchase #3 $208.62   7.289%   $223.8263   $223.83   $223.85   $223.80  
  Purchase #4 $165.56   3.235%   $170.9159   $170.92   $170.90   $170.90  
  Purchase #5 $197.52   13.603%   $224.3886   $224.39   $224.40   $224.40  
  Purchase #6 $173.26   12.126%   $194.2695   $194.27   $194.25   $194.30  
  Purchase #7 $81.57   4.775%   $85.465   $85.47   $85.45   $85.50  
  7 purchase totals = $1,137.73       $1,233.4995   $1,233.52   $1,233.50   $1,233.50