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	$6.48	13.281%	$7.3406	$7.34	$7.35	$7.30
Purchase #2	$139.98	8.128%	$151.3576	$151.36	$151.35	$151.40
Purchase #3	$26.56	9.765%	$29.1536	$29.15	$29.15	$29.20
Purchase #4	$27.60	13.194%	$31.2415	$31.24	$31.25	$31.20
Purchase #5	$95.57	5.601%	$100.9229	$100.92	$100.90	$100.90
Purchase #6	$246.46	6.404%	$262.2433	$262.24	$262.25	$262.20
Purchase #7	$147.39	8.169%	$159.4303	$159.43	$159.45	$159.40
7 purchase totals =	$690.04		$741.6898	$741.68	$741.70	$741.60