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	$27.81	13.103%	$31.4539	$31.45	$31.45	$31.50
Purchase #2	$69.46	6.620%	$74.0583	$74.06	$74.05	$74.10
Purchase #3	$157.77	6.335%	$167.7647	$167.76	$167.75	$167.80
Purchase #4	$55.56	13.342%	$62.9728	$62.97	$62.95	$63.00
Purchase #5	$79.32	3.865%	$82.3857	$82.39	$82.40	$82.40
Purchase #6	$36.49	5.341%	$38.4389	$38.44	$38.45	$38.40
Purchase #7	$30.98	13.814%	$35.2596	$35.26	$35.25	$35.30
7 purchase totals =	$457.39		$492.3339	$492.33	$492.30	$492.50