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	$67.40	7.319%	$72.333	$72.33	$72.35	$72.30
Purchase #2	$93.42	9.740%	$102.5191	$102.52	$102.50	$102.50
Purchase #3	$120.44	5.557%	$127.1329	$127.13	$127.15	$127.10
Purchase #4	$143.67	13.671%	$163.3111	$163.31	$163.30	$163.30
Purchase #5	$110.47	11.871%	$123.5839	$123.58	$123.60	$123.60
Purchase #6	$151.66	5.649%	$160.2273	$160.23	$160.25	$160.20
Purchase #7	$150.48	11.205%	$167.3413	$167.34	$167.35	$167.30
7 purchase totals =	$837.54		$916.4486	$916.44	$916.50	$916.30