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	$41.30	10.810%	$45.7645	$45.76	$45.75	$45.80
Purchase #2	$184.55	6.717%	$196.9462	$196.95	$196.95	$196.90
Purchase #3	$37.81	7.375%	$40.5985	$40.60	$40.60	$40.60
Purchase #4	$75.83	9.338%	$82.911	$82.91	$82.90	$82.90
Purchase #5	$17.42	12.565%	$19.6088	$19.61	$19.60	$19.60
Purchase #6	$237.33	8.553%	$257.6288	$257.63	$257.65	$257.60
Purchase #7	$22.97	11.544%	$25.6217	$25.62	$25.60	$25.60
7 purchase totals =	$617.21		$669.0795	$669.08	$669.05	$669.00