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	$53.41	4.160%	$55.6319	$55.63	$55.65	$55.60
Purchase #2	$152.79	12.736%	$172.2493	$172.25	$172.25	$172.20
Purchase #3	$106.40	3.286%	$109.8963	$109.90	$109.90	$109.90
Purchase #4	$201.28	11.104%	$223.6301	$223.63	$223.65	$223.60
Purchase #5	$146.74	3.125%	$151.3256	$151.33	$151.35	$151.30
Purchase #6	$204.59	7.337%	$219.6008	$219.60	$219.60	$219.60
Purchase #7	$7.75	10.389%	$8.5551	$8.56	$8.55	$8.60
7 purchase totals =	$872.96		$940.8891	$940.90	$940.95	$940.80