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 $119.39   13.866%   $135.9446   $135.94   $135.95   $135.90  
  Purchase #2 $206.93   10.583%   $228.8294   $228.83   $228.85   $228.80  
  Purchase #3 $176.27   10.216%   $194.2777   $194.28   $194.30   $194.30  
  Purchase #4 $135.93   4.654%   $142.2562   $142.26   $142.25   $142.30  
  Purchase #5 $197.41   9.260%   $215.6902   $215.69   $215.70   $215.70  
  Purchase #6 $58.31   5.735%   $61.6541   $61.65   $61.65   $61.70  
  Purchase #7 $225.57   9.730%   $247.518   $247.52   $247.50   $247.50  
  7 purchase totals = $1,119.81       $1,226.1702   $1,226.17   $1,226.20   $1,226.20