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	$168.29	13.830%	$191.5645	$191.56	$191.55	$191.60
Purchase #2	$147.59	13.743%	$167.8733	$167.87	$167.85	$167.90
Purchase #3	$90.69	13.562%	$102.9894	$102.99	$103.00	$103.00
Purchase #4	$250.99	9.607%	$275.1026	$275.10	$275.10	$275.10
Purchase #5	$245.69	12.129%	$275.4897	$275.49	$275.50	$275.50
Purchase #6	$11.44	6.222%	$12.1518	$12.15	$12.15	$12.20
Purchase #7	$5.46	4.182%	$5.6883	$5.69	$5.70	$5.70
7 purchase totals =	$920.15		$1,030.8596	$1,030.85	$1,030.85	$1,031.00