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	$137.46	9.199%	$150.1049	$150.10	$150.10	$150.10
Purchase #2	$122.81	13.527%	$139.4225	$139.42	$139.40	$139.40
Purchase #3	$229.97	11.366%	$256.1084	$256.11	$256.10	$256.10
Purchase #4	$58.70	4.463%	$61.3198	$61.32	$61.30	$61.30
Purchase #5	$112.43	6.863%	$120.1461	$120.15	$120.15	$120.10
Purchase #6	$153.62	12.430%	$172.715	$172.72	$172.70	$172.70
Purchase #7	$36.61	11.734%	$40.9058	$40.91	$40.90	$40.90
7 purchase totals =	$851.60		$940.7225	$940.73	$940.65	$940.60