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	$11.97	5.219%	$12.5947	$12.59	$12.60	$12.60
Purchase #2	$247.58	11.202%	$275.3139	$275.31	$275.30	$275.30
Purchase #3	$59.53	10.156%	$65.5759	$65.58	$65.60	$65.60
Purchase #4	$43.88	4.719%	$45.9507	$45.95	$45.95	$46.00
Purchase #5	$172.91	8.773%	$188.0794	$188.08	$188.10	$188.10
Purchase #6	$117.63	11.415%	$131.0575	$131.06	$131.05	$131.10
Purchase #7	$69.97	5.452%	$73.7848	$73.78	$73.80	$73.80
7 purchase totals =	$723.47		$792.3569	$792.35	$792.40	$792.50