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	$30.98	5.322%	$32.6288	$32.63	$32.65	$32.60
Purchase #2	$141.46	3.509%	$146.4238	$146.42	$146.40	$146.40
Purchase #3	$75.52	9.545%	$82.7284	$82.73	$82.75	$82.70
Purchase #4	$79.59	12.391%	$89.452	$89.45	$89.45	$89.50
Purchase #5	$139.62	13.842%	$158.9462	$158.95	$158.95	$158.90
Purchase #6	$228.73	6.801%	$244.2859	$244.29	$244.30	$244.30
Purchase #7	$186.77	4.825%	$195.7817	$195.78	$195.80	$195.80
7 purchase totals =	$882.67		$950.2468	$950.25	$950.30	$950.20