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 $54.94   11.241%   $61.1158   $61.12   $61.10   $61.10  
  Purchase #2 $152.94   11.393%   $170.3645   $170.36   $170.35   $170.40  
  Purchase #3 $200.87   12.722%   $226.4247   $226.42   $226.40   $226.40  
  Purchase #4 $114.34   5.355%   $120.4629   $120.46   $120.45   $120.50  
  Purchase #5 $48.50   5.796%   $51.3111   $51.31   $51.30   $51.30  
  Purchase #6 $38.29   11.460%   $42.678   $42.68   $42.70   $42.70  
  Purchase #7 $228.43   10.405%   $252.1981   $252.20   $252.20   $252.20  
  7 purchase totals = $838.31       $924.5551   $924.55   $924.50   $924.60