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	$49.75	10.773%	$55.1096	$55.11	$55.10	$55.10
Purchase #2	$117.69	9.505%	$128.8764	$128.88	$128.90	$128.90
Purchase #3	$99.75	6.172%	$105.9066	$105.91	$105.90	$105.90
Purchase #4	$139.50	7.822%	$150.4117	$150.41	$150.40	$150.40
Purchase #5	$74.80	5.467%	$78.8893	$78.89	$78.90	$78.90
Purchase #6	$210.72	13.495%	$239.1567	$239.16	$239.15	$239.20
Purchase #7	$60.55	13.218%	$68.5535	$68.55	$68.55	$68.60
7 purchase totals =	$752.76		$826.9038	$826.91	$826.90	$827.00