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	$207.89	13.744%	$236.4624	$236.46	$236.45	$236.50
Purchase #2	$233.42	10.234%	$257.3082	$257.31	$257.30	$257.30
Purchase #3	$57.49	11.841%	$64.2974	$64.30	$64.30	$64.30
Purchase #4	$104.46	6.145%	$110.8791	$110.88	$110.90	$110.90
Purchase #5	$105.99	5.590%	$111.9148	$111.91	$111.90	$111.90
Purchase #6	$31.66	13.305%	$35.8724	$35.87	$35.85	$35.90
Purchase #7	$19.81	3.172%	$20.4384	$20.44	$20.45	$20.40
7 purchase totals =	$760.72		$837.1727	$837.17	$837.15	$837.20