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 $114.67   4.195%   $119.4804   $119.48   $119.50   $119.50  
  Purchase #2 $55.40   4.848%   $58.0858   $58.09   $58.10   $58.10  
  Purchase #3 $202.60   8.552%   $219.9264   $219.93   $219.95   $219.90  
  Purchase #4 $180.70   11.493%   $201.4679   $201.47   $201.45   $201.50  
  Purchase #5 $226.92   9.664%   $248.8495   $248.85   $248.85   $248.80  
  Purchase #6 $100.52   11.796%   $112.3773   $112.38   $112.40   $112.40  
  Purchase #7 $83.67   11.758%   $93.5079   $93.51   $93.50   $93.50  
  7 purchase totals = $964.48       $1,053.6952   $1,053.71   $1,053.75   $1,053.70