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	$227.43	9.393%	$248.7925	$248.79	$248.80	$248.80
Purchase #2	$99.65	10.702%	$110.3145	$110.31	$110.30	$110.30
Purchase #3	$77.78	9.390%	$85.0835	$85.08	$85.10	$85.10
Purchase #4	$69.42	4.187%	$72.3266	$72.33	$72.35	$72.30
Purchase #5	$219.83	4.423%	$229.5531	$229.55	$229.55	$229.60
Purchase #6	$175.33	9.189%	$191.4411	$191.44	$191.45	$191.40
Purchase #7	$126.27	8.684%	$137.2353	$137.24	$137.25	$137.20
7 purchase totals =	$995.71		$1,074.7466	$1,074.74	$1,074.80	$1,074.70