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 $226.76   11.852%   $253.6356   $253.64   $253.65   $253.60  
  Purchase #2 $239.69   5.428%   $252.7004   $252.70   $252.70   $252.70  
  Purchase #3 $18.55   5.719%   $19.6109   $19.61   $19.60   $19.60  
  Purchase #4 $80.82   4.750%   $84.659   $84.66   $84.65   $84.70  
  Purchase #5 $169.81   4.120%   $176.8062   $176.81   $176.80   $176.80  
  Purchase #6 $143.64   9.208%   $156.8664   $156.87   $156.85   $156.90  
  Purchase #7 $243.91   8.233%   $263.9911   $263.99   $264.00   $264.00  
  7 purchase totals = $1,123.18       $1,208.2696   $1,208.28   $1,208.25   $1,208.30