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	$45.41	6.598%	$48.4062	$48.41	$48.40	$48.40
Purchase #2	$113.94	11.531%	$127.0784	$127.08	$127.10	$127.10
Purchase #3	$249.42	9.783%	$273.8208	$273.82	$273.80	$273.80
Purchase #4	$29.47	10.459%	$32.5523	$32.55	$32.55	$32.60
Purchase #5	$84.83	5.136%	$89.1869	$89.19	$89.20	$89.20
Purchase #6	$42.37	13.379%	$48.0387	$48.04	$48.05	$48.00
Purchase #7	$151.66	13.537%	$172.1902	$172.19	$172.20	$172.20
7 purchase totals =	$717.10		$791.2735	$791.28	$791.30	$791.30