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	$189.41	13.271%	$214.5466	$214.55	$214.55	$214.50
Purchase #2	$141.95	4.159%	$147.8537	$147.85	$147.85	$147.90
Purchase #3	$85.30	13.232%	$96.5869	$96.59	$96.60	$96.60
Purchase #4	$9.33	13.592%	$10.5981	$10.60	$10.60	$10.60
Purchase #5	$89.97	10.848%	$99.7299	$99.73	$99.75	$99.70
Purchase #6	$82.56	4.618%	$86.3726	$86.37	$86.35	$86.40
Purchase #7	$11.88	10.439%	$13.1202	$13.12	$13.10	$13.10
7 purchase totals =	$610.40		$668.8080	$668.81	$668.80	$668.80