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	$75.52	4.419%	$78.8572	$78.86	$78.85	$78.90
Purchase #2	$183.29	7.364%	$196.7875	$196.79	$196.80	$196.80
Purchase #3	$196.94	9.256%	$215.1688	$215.17	$215.15	$215.20
Purchase #4	$198.25	5.599%	$209.35	$209.35	$209.35	$209.40
Purchase #5	$35.65	4.821%	$37.3687	$37.37	$37.35	$37.40
Purchase #6	$20.51	5.560%	$21.6504	$21.65	$21.65	$21.70
Purchase #7	$192.38	13.599%	$218.5418	$218.54	$218.55	$218.50
7 purchase totals =	$902.54		$977.7244	$977.73	$977.70	$977.90