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	$156.91	6.107%	$166.4925	$166.49	$166.50	$166.50
Purchase #2	$110.92	11.265%	$123.4151	$123.42	$123.40	$123.40
Purchase #3	$138.84	10.741%	$153.7528	$153.75	$153.75	$153.80
Purchase #4	$168.56	11.785%	$188.4248	$188.42	$188.40	$188.40
Purchase #5	$176.78	7.433%	$189.9201	$189.92	$189.90	$189.90
Purchase #6	$248.60	4.696%	$260.2743	$260.27	$260.25	$260.30
Purchase #7	$82.44	3.328%	$85.1836	$85.18	$85.20	$85.20
7 purchase totals =	$1,083.05		$1,167.4632	$1,167.45	$1,167.40	$1,167.50