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	$69.77	11.449%	$77.758	$77.76	$77.75	$77.80
Purchase #2	$97.31	8.543%	$105.6232	$105.62	$105.60	$105.60
Purchase #3	$117.85	11.561%	$131.4746	$131.47	$131.45	$131.50
Purchase #4	$118.85	7.581%	$127.86	$127.86	$127.85	$127.90
Purchase #5	$81.72	7.356%	$87.7313	$87.73	$87.75	$87.70
Purchase #6	$136.36	3.743%	$141.464	$141.46	$141.45	$141.50
Purchase #7	$142.74	4.179%	$148.7051	$148.71	$148.70	$148.70
7 purchase totals =	$764.60		$820.6162	$820.61	$820.55	$820.70