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 $67.28   10.497%   $74.3424   $74.34   $74.35   $74.30  
  Purchase #2 $47.71   3.848%   $49.5459   $49.55   $49.55   $49.50  
  Purchase #3 $118.83   12.215%   $133.3451   $133.35   $133.35   $133.30  
  Purchase #4 $221.51   10.466%   $244.6932   $244.69   $244.70   $244.70  
  Purchase #5 $226.79   5.241%   $238.6761   $238.68   $238.70   $238.70  
  Purchase #6 $202.45   13.384%   $229.5459   $229.55   $229.55   $229.50  
  Purchase #7 $32.54   12.202%   $36.5105   $36.51   $36.50   $36.50  
  7 purchase totals = $917.11       $1,006.6591   $1,006.67   $1,006.70   $1,006.50