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	$37.72	3.819%	$39.1605	$39.16	$39.15	$39.20
Purchase #2	$92.27	6.451%	$98.2223	$98.22	$98.20	$98.20
Purchase #3	$104.37	6.469%	$111.1217	$111.12	$111.10	$111.10
Purchase #4	$97.58	13.108%	$110.3708	$110.37	$110.35	$110.40
Purchase #5	$160.85	4.523%	$168.1252	$168.13	$168.15	$168.10
Purchase #6	$30.84	13.837%	$35.1073	$35.11	$35.10	$35.10
Purchase #7	$162.87	7.789%	$175.5559	$175.56	$175.55	$175.60
7 purchase totals =	$686.50		$737.6637	$737.67	$737.60	$737.70