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	$46.69	7.847%	$50.3538	$50.35	$50.35	$50.40
Purchase #2	$236.43	13.617%	$268.6247	$268.62	$268.60	$268.60
Purchase #3	$104.64	13.133%	$118.3824	$118.38	$118.40	$118.40
Purchase #4	$149.83	11.308%	$166.7728	$166.77	$166.75	$166.80
Purchase #5	$169.35	6.300%	$180.0191	$180.02	$180.00	$180.00
Purchase #6	$223.45	6.500%	$237.9743	$237.97	$237.95	$238.00
Purchase #7	$56.78	13.434%	$64.4078	$64.41	$64.40	$64.40
7 purchase totals =	$987.17		$1,086.5349	$1,086.52	$1,086.45	$1,086.60