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	$202.90	12.274%	$227.8039	$227.80	$227.80	$227.80
Purchase #2	$166.87	6.768%	$178.1638	$178.16	$178.15	$178.20
Purchase #3	$58.36	11.508%	$65.0761	$65.08	$65.10	$65.10
Purchase #4	$153.76	9.141%	$167.8152	$167.82	$167.80	$167.80
Purchase #5	$143.50	10.542%	$158.6278	$158.63	$158.65	$158.60
Purchase #6	$89.76	10.858%	$99.5061	$99.51	$99.50	$99.50
Purchase #7	$188.61	6.205%	$200.3133	$200.31	$200.30	$200.30
7 purchase totals =	$1,003.76		$1,097.3062	$1,097.31	$1,097.30	$1,097.30