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 $111.85   13.103%   $126.5057   $126.51   $126.50   $126.50  
  Purchase #2 $126.53   7.319%   $135.7907   $135.79   $135.80   $135.80  
  Purchase #3 $73.74   7.840%   $79.5212   $79.52   $79.50   $79.50  
  Purchase #4 $107.37   7.350%   $115.2617   $115.26   $115.25   $115.30  
  Purchase #5 $182.26   5.695%   $192.6397   $192.64   $192.65   $192.60  
  Purchase #6 $239.95   5.787%   $253.8359   $253.84   $253.85   $253.80  
  Purchase #7 $115.26   7.503%   $123.908   $123.91   $123.90   $123.90  
  7 purchase totals = $956.96       $1,027.4629   $1,027.47   $1,027.45   $1,027.40