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 $191.33   3.164%   $197.3837   $197.38   $197.40   $197.40  
  Purchase #2 $174.78   4.677%   $182.9545   $182.95   $182.95   $183.00  
  Purchase #3 $58.78   6.632%   $62.6783   $62.68   $62.70   $62.70  
  Purchase #4 $72.71   13.855%   $82.784   $82.78   $82.80   $82.80  
  Purchase #5 $246.72   10.717%   $273.161   $273.16   $273.15   $273.20  
  Purchase #6 $30.79   13.241%   $34.8669   $34.87   $34.85   $34.90  
  Purchase #7 $168.96   13.775%   $192.2342   $192.23   $192.25   $192.20  
  7 purchase totals = $944.07       $1,026.0626   $1,026.05   $1,026.10   $1,026.20