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	$210.32	3.672%	$218.043	$218.04	$218.05	$218.00
Purchase #2	$194.73	6.271%	$206.9415	$206.94	$206.95	$206.90
Purchase #3	$142.84	11.259%	$158.9224	$158.92	$158.90	$158.90
Purchase #4	$72.91	12.815%	$82.2534	$82.25	$82.25	$82.30
Purchase #5	$157.99	12.708%	$178.0674	$178.07	$178.05	$178.10
Purchase #6	$39.27	11.450%	$43.7664	$43.77	$43.75	$43.80
Purchase #7	$35.64	12.692%	$40.1634	$40.16	$40.15	$40.20
7 purchase totals =	$853.70		$928.1575	$928.15	$928.10	$928.20