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 $54.60   13.310%   $61.8673   $61.87   $61.85   $61.90  
  Purchase #2 $58.75   10.328%   $64.8177   $64.82   $64.80   $64.80  
  Purchase #3 $165.47   4.269%   $172.5339   $172.53   $172.55   $172.50  
  Purchase #4 $201.61   3.233%   $208.1281   $208.13   $208.15   $208.10  
  Purchase #5 $14.32   11.312%   $15.9399   $15.94   $15.95   $15.90  
  Purchase #6 $22.45   4.173%   $23.3868   $23.39   $23.40   $23.40  
  Purchase #7 $243.54   5.723%   $257.4778   $257.48   $257.50   $257.50  
  7 purchase totals = $760.74       $804.1515   $804.16   $804.20   $804.10