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	$33.31	9.667%	$36.5301	$36.53	$36.55	$36.50
Purchase #2	$89.84	7.432%	$96.5169	$96.52	$96.50	$96.50
Purchase #3	$99.97	10.162%	$110.129	$110.13	$110.15	$110.10
Purchase #4	$56.75	11.568%	$63.3148	$63.31	$63.30	$63.30
Purchase #5	$215.26	8.529%	$233.6195	$233.62	$233.60	$233.60
Purchase #6	$29.75	12.530%	$33.4777	$33.48	$33.50	$33.50
Purchase #7	$69.72	3.775%	$72.3519	$72.35	$72.35	$72.40
7 purchase totals =	$594.60		$645.9399	$645.94	$645.95	$645.90