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	$151.54	13.620%	$172.1797	$172.18	$172.20	$172.20
Purchase #2	$209.57	10.740%	$232.0778	$232.08	$232.10	$232.10
Purchase #3	$9.86	10.126%	$10.8584	$10.86	$10.85	$10.90
Purchase #4	$99.45	12.135%	$111.5183	$111.52	$111.50	$111.50
Purchase #5	$233.32	12.104%	$261.5611	$261.56	$261.55	$261.60
Purchase #6	$38.89	6.254%	$41.3222	$41.32	$41.30	$41.30
Purchase #7	$63.57	5.588%	$67.1223	$67.12	$67.10	$67.10
7 purchase totals =	$806.20		$896.6398	$896.64	$896.60	$896.70