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 $86.67   13.797%   $98.6279   $98.63   $98.65   $98.60  
  Purchase #2 $170.98   5.469%   $180.3309   $180.33   $180.35   $180.30  
  Purchase #3 $126.99   11.565%   $141.6764   $141.68   $141.70   $141.70  
  Purchase #4 $184.93   5.775%   $195.6097   $195.61   $195.60   $195.60  
  Purchase #5 $130.25   3.512%   $134.8244   $134.82   $134.80   $134.80  
  Purchase #6 $248.76   5.451%   $262.3199   $262.32   $262.30   $262.30  
  Purchase #7 $42.27   10.740%   $46.8098   $46.81   $46.80   $46.80  
  7 purchase totals = $990.85       $1,060.1990   $1,060.20   $1,060.20   $1,060.10