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	$225.29	13.460%	$255.614	$255.61	$255.60	$255.60
Purchase #2	$236.68	5.831%	$250.4808	$250.48	$250.50	$250.50
Purchase #3	$207.41	9.632%	$227.3877	$227.39	$227.40	$227.40
Purchase #4	$237.54	13.362%	$269.2801	$269.28	$269.30	$269.30
Purchase #5	$140.88	11.104%	$156.5233	$156.52	$156.50	$156.50
Purchase #6	$12.69	8.188%	$13.7291	$13.73	$13.75	$13.70
Purchase #7	$43.74	10.470%	$48.3196	$48.32	$48.30	$48.30
7 purchase totals =	$1,104.23		$1,221.3346	$1,221.33	$1,221.35	$1,221.30