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	$58.64	11.782%	$65.549	$65.55	$65.55	$65.50
Purchase #2	$114.69	7.583%	$123.3869	$123.39	$123.40	$123.40
Purchase #3	$25.46	7.339%	$27.3285	$27.33	$27.35	$27.30
Purchase #4	$64.30	13.712%	$73.1168	$73.12	$73.10	$73.10
Purchase #5	$57.39	6.467%	$61.1014	$61.10	$61.10	$61.10
Purchase #6	$36.50	11.810%	$40.8107	$40.81	$40.80	$40.80
Purchase #7	$114.91	3.413%	$118.8319	$118.83	$118.85	$118.80
7 purchase totals =	$471.89		$510.1252	$510.13	$510.15	$510.00