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	$207.27	6.813%	$221.3913	$221.39	$221.40	$221.40
Purchase #2	$68.66	13.783%	$78.1234	$78.12	$78.10	$78.10
Purchase #3	$227.79	10.829%	$252.4574	$252.46	$252.45	$252.50
Purchase #4	$240.81	5.421%	$253.8643	$253.86	$253.85	$253.90
Purchase #5	$165.71	3.467%	$171.4552	$171.46	$171.45	$171.50
Purchase #6	$52.54	10.351%	$57.9784	$57.98	$58.00	$58.00
Purchase #7	$248.31	10.130%	$273.4638	$273.46	$273.45	$273.50
7 purchase totals =	$1,211.09		$1,308.7338	$1,308.73	$1,308.70	$1,308.90