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	$220.44	4.319%	$229.9608	$229.96	$229.95	$230.00
Purchase #2	$51.64	5.697%	$54.5819	$54.58	$54.60	$54.60
Purchase #3	$144.41	8.311%	$156.4119	$156.41	$156.40	$156.40
Purchase #4	$27.61	6.564%	$29.4223	$29.42	$29.40	$29.40
Purchase #5	$45.84	10.297%	$50.5601	$50.56	$50.55	$50.60
Purchase #6	$79.44	12.646%	$89.486	$89.49	$89.50	$89.50
Purchase #7	$61.44	6.808%	$65.6228	$65.62	$65.60	$65.60
7 purchase totals =	$630.82		$676.0458	$676.04	$676.00	$676.10