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	$42.33	6.726%	$45.1771	$45.18	$45.20	$45.20
Purchase #2	$149.58	10.649%	$165.5088	$165.51	$165.50	$165.50
Purchase #3	$249.88	7.460%	$268.521	$268.52	$268.50	$268.50
Purchase #4	$209.87	12.588%	$236.2884	$236.29	$236.30	$236.30
Purchase #5	$164.70	6.772%	$175.8535	$175.85	$175.85	$175.90
Purchase #6	$139.98	13.279%	$158.5679	$158.57	$158.55	$158.60
Purchase #7	$237.89	4.198%	$247.8766	$247.88	$247.90	$247.90
7 purchase totals =	$1,194.23		$1,297.7933	$1,297.80	$1,297.80	$1,297.90