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 $142.73   7.154%   $152.9409   $152.94   $152.95   $152.90  
  Purchase #2 $106.93   11.648%   $119.3852   $119.39   $119.40   $119.40  
  Purchase #3 $86.63   11.451%   $96.55   $96.55   $96.55   $96.60  
  Purchase #4 $119.57   7.715%   $128.7948   $128.79   $128.80   $128.80  
  Purchase #5 $208.86   8.821%   $227.2835   $227.28   $227.30   $227.30  
  Purchase #6 $26.65   11.654%   $29.7558   $29.76   $29.75   $29.80  
  Purchase #7 $204.80   5.730%   $216.535   $216.54   $216.55   $216.50  
  7 purchase totals = $896.17       $971.2452   $971.25   $971.30   $971.30