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	$35.66	7.685%	$38.4005	$38.40	$38.40	$38.40
Purchase #2	$114.60	11.140%	$127.3664	$127.37	$127.35	$127.40
Purchase #3	$65.85	8.243%	$71.278	$71.28	$71.30	$71.30
Purchase #4	$243.36	11.561%	$271.4948	$271.49	$271.50	$271.50
Purchase #5	$114.92	8.112%	$124.2423	$124.24	$124.25	$124.20
Purchase #6	$60.98	5.401%	$64.2735	$64.27	$64.25	$64.30
Purchase #7	$199.98	6.315%	$212.6087	$212.61	$212.60	$212.60
7 purchase totals =	$835.35		$909.6642	$909.66	$909.65	$909.70