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 $85.85   5.562%   $90.625   $90.63   $90.65   $90.60  
  Purchase #2 $117.40   13.301%   $133.0154   $133.02   $133.00   $133.00  
  Purchase #3 $144.47   8.626%   $156.932   $156.93   $156.95   $156.90  
  Purchase #4 $172.64   3.738%   $179.0933   $179.09   $179.10   $179.10  
  Purchase #5 $56.98   5.566%   $60.1515   $60.15   $60.15   $60.20  
  Purchase #6 $6.35   11.269%   $7.0656   $7.07   $7.05   $7.10  
  Purchase #7 $237.64   4.556%   $248.4669   $248.47   $248.45   $248.50  
  7 purchase totals = $821.33       $875.3497   $875.36   $875.35   $875.40