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	$65.99	9.261%	$72.1013	$72.10	$72.10	$72.10
Purchase #2	$88.45	6.383%	$94.0958	$94.10	$94.10	$94.10
Purchase #3	$210.98	3.219%	$217.7714	$217.77	$217.75	$217.80
Purchase #4	$161.89	6.597%	$172.5699	$172.57	$172.55	$172.60
Purchase #5	$40.75	6.277%	$43.3079	$43.31	$43.30	$43.30
Purchase #6	$199.78	6.526%	$212.8176	$212.82	$212.80	$212.80
Purchase #7	$169.43	5.214%	$178.2641	$178.26	$178.25	$178.30
7 purchase totals =	$937.27		$990.9280	$990.93	$990.85	$991.00