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 $70.99   6.431%   $75.5554   $75.56   $75.55   $75.60  
  Purchase #2 $68.41   7.278%   $73.3889   $73.39   $73.40   $73.40  
  Purchase #3 $154.67   10.422%   $170.7897   $170.79   $170.80   $170.80  
  Purchase #4 $133.47   13.469%   $151.4471   $151.45   $151.45   $151.40  
  Purchase #5 $224.55   5.794%   $237.5604   $237.56   $237.55   $237.60  
  Purchase #6 $55.50   12.531%   $62.4547   $62.45   $62.45   $62.50  
  Purchase #7 $222.43   11.581%   $248.1896   $248.19   $248.20   $248.20  
  7 purchase totals = $930.02       $1,019.3858   $1,019.39   $1,019.40   $1,019.50