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	$19.98	9.590%	$21.8961	$21.90	$21.90	$21.90
Purchase #2	$130.94	8.774%	$142.4287	$142.43	$142.45	$142.40
Purchase #3	$49.99	4.106%	$52.0426	$52.04	$52.05	$52.00
Purchase #4	$138.73	13.719%	$157.7624	$157.76	$157.75	$157.80
Purchase #5	$80.81	5.583%	$85.3216	$85.32	$85.30	$85.30
Purchase #6	$105.76	5.644%	$111.7291	$111.73	$111.75	$111.70
Purchase #7	$35.48	13.497%	$40.2687	$40.27	$40.25	$40.30
7 purchase totals =	$561.69		$611.4492	$611.45	$611.45	$611.40