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 $58.76   5.207%   $61.8196   $61.82   $61.80   $61.80  
  Purchase #2 $62.94   13.126%   $71.2015   $71.20   $71.20   $71.20  
  Purchase #3 $7.93   6.372%   $8.4353   $8.44   $8.45   $8.40  
  Purchase #4 $68.61   7.610%   $73.8312   $73.83   $73.85   $73.80  
  Purchase #5 $170.82   8.211%   $184.846   $184.85   $184.85   $184.80  
  Purchase #6 $127.71   12.852%   $144.1233   $144.12   $144.10   $144.10  
  Purchase #7 $60.37   13.611%   $68.587   $68.59   $68.60   $68.60  
  7 purchase totals = $557.14       $612.8439   $612.85   $612.85   $612.70