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	$229.60	5.531%	$242.2992	$242.30	$242.30	$242.30
Purchase #2	$117.37	7.214%	$125.8371	$125.84	$125.85	$125.80
Purchase #3	$116.79	6.712%	$124.6289	$124.63	$124.65	$124.60
Purchase #4	$47.79	10.321%	$52.7224	$52.72	$52.70	$52.70
Purchase #5	$103.85	6.861%	$110.9751	$110.98	$111.00	$111.00
Purchase #6	$132.37	7.653%	$142.5003	$142.50	$142.50	$142.50
Purchase #7	$86.61	3.634%	$89.7574	$89.76	$89.75	$89.80
7 purchase totals =	$834.38		$888.7204	$888.73	$888.75	$888.70