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 $59.58   3.180%   $61.4746   $61.47   $61.45   $61.50  
  Purchase #2 $174.42   5.444%   $183.9154   $183.92   $183.90   $183.90  
  Purchase #3 $239.85   4.805%   $251.3748   $251.37   $251.35   $251.40  
  Purchase #4 $153.83   4.848%   $161.2877   $161.29   $161.30   $161.30  
  Purchase #5 $156.39   13.483%   $177.4761   $177.48   $177.50   $177.50  
  Purchase #6 $231.65   12.809%   $261.322   $261.32   $261.30   $261.30  
  Purchase #7 $174.96   10.223%   $192.8462   $192.85   $192.85   $192.80  
  7 purchase totals = $1,190.68       $1,289.6968   $1,289.70   $1,289.65   $1,289.70