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 $50.90   13.167%   $57.602   $57.60   $57.60   $57.60  
  Purchase #2 $215.88   9.169%   $235.674   $235.67   $235.65   $235.70  
  Purchase #3 $61.76   8.415%   $66.9571   $66.96   $66.95   $67.00  
  Purchase #4 $222.93   12.260%   $250.2612   $250.26   $250.25   $250.30  
  Purchase #5 $6.76   11.337%   $7.5264   $7.53   $7.55   $7.50  
  Purchase #6 $218.80   11.504%   $243.9708   $243.97   $243.95   $244.00  
  Purchase #7 $42.83   3.211%   $44.2053   $44.21   $44.20   $44.20  
  7 purchase totals = $819.86       $906.1968   $906.20   $906.15   $906.30