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	$156.77	12.166%	$175.8426	$175.84	$175.85	$175.80
Purchase #2	$191.81	7.335%	$205.8793	$205.88	$205.90	$205.90
Purchase #3	$54.70	5.338%	$57.6199	$57.62	$57.60	$57.60
Purchase #4	$179.42	8.605%	$194.8591	$194.86	$194.85	$194.90
Purchase #5	$89.82	5.492%	$94.7529	$94.75	$94.75	$94.80
Purchase #6	$53.93	10.753%	$59.7291	$59.73	$59.75	$59.70
Purchase #7	$67.83	5.376%	$71.4765	$71.48	$71.50	$71.50
7 purchase totals =	$794.28		$860.1594	$860.16	$860.20	$860.20