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	$131.91	7.568%	$141.8929	$141.89	$141.90	$141.90
Purchase #2	$86.38	11.667%	$96.458	$96.46	$96.45	$96.50
Purchase #3	$34.96	6.335%	$37.1747	$37.17	$37.15	$37.20
Purchase #4	$68.45	4.446%	$71.4933	$71.49	$71.50	$71.50
Purchase #5	$107.91	10.152%	$118.865	$118.87	$118.85	$118.90
Purchase #6	$189.30	13.560%	$214.9691	$214.97	$214.95	$215.00
Purchase #7	$62.75	9.826%	$68.9158	$68.92	$68.90	$68.90
7 purchase totals =	$681.66		$749.7688	$749.77	$749.70	$749.90