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	$33.75	6.121%	$35.8158	$35.82	$35.80	$35.80
Purchase #2	$32.29	11.441%	$35.9843	$35.98	$36.00	$36.00
Purchase #3	$84.31	8.728%	$91.6686	$91.67	$91.65	$91.70
Purchase #4	$82.33	11.105%	$91.4727	$91.47	$91.45	$91.50
Purchase #5	$21.34	11.153%	$23.7201	$23.72	$23.70	$23.70
Purchase #6	$89.72	11.808%	$100.3141	$100.31	$100.30	$100.30
Purchase #7	$71.64	11.426%	$79.8256	$79.83	$79.85	$79.80
7 purchase totals =	$415.38		$458.8012	$458.80	$458.75	$458.80