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	$124.53	5.347%	$131.1886	$131.19	$131.20	$131.20
Purchase #2	$100.27	10.501%	$110.7994	$110.80	$110.80	$110.80
Purchase #3	$48.84	4.647%	$51.1096	$51.11	$51.10	$51.10
Purchase #4	$141.38	8.771%	$153.7804	$153.78	$153.80	$153.80
Purchase #5	$43.42	5.802%	$45.9392	$45.94	$45.95	$45.90
Purchase #6	$90.90	10.772%	$100.6917	$100.69	$100.70	$100.70
Purchase #7	$33.96	4.233%	$35.3975	$35.40	$35.40	$35.40
7 purchase totals =	$583.30		$628.9064	$628.91	$628.95	$628.90