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	$133.41	9.843%	$146.5415	$146.54	$146.55	$146.50
Purchase #2	$76.46	3.455%	$79.1017	$79.10	$79.10	$79.10
Purchase #3	$239.39	9.143%	$261.2774	$261.28	$261.30	$261.30
Purchase #4	$49.39	10.274%	$54.4643	$54.46	$54.45	$54.50
Purchase #5	$99.58	4.149%	$103.7116	$103.71	$103.70	$103.70
Purchase #6	$147.76	4.418%	$154.288	$154.29	$154.30	$154.30
Purchase #7	$172.79	11.398%	$192.4846	$192.48	$192.50	$192.50
7 purchase totals =	$918.78		$991.8691	$991.86	$991.90	$991.90