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	$152.79	8.273%	$165.4303	$165.43	$165.45	$165.40
Purchase #2	$81.87	11.184%	$91.0263	$91.03	$91.05	$91.00
Purchase #3	$65.36	9.617%	$71.6457	$71.65	$71.65	$71.60
Purchase #4	$202.91	3.728%	$210.4745	$210.47	$210.45	$210.50
Purchase #5	$235.86	8.589%	$256.118	$256.12	$256.10	$256.10
Purchase #6	$52.60	13.791%	$59.8541	$59.85	$59.85	$59.90
Purchase #7	$60.71	8.449%	$65.8394	$65.84	$65.85	$65.80
7 purchase totals =	$852.10		$920.3883	$920.39	$920.40	$920.30