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	$150.64	3.666%	$156.1625	$156.16	$156.15	$156.20
Purchase #2	$179.53	11.360%	$199.9246	$199.92	$199.90	$199.90
Purchase #3	$148.88	8.837%	$162.0365	$162.04	$162.05	$162.00
Purchase #4	$11.49	10.565%	$12.7039	$12.70	$12.70	$12.70
Purchase #5	$38.30	5.496%	$40.405	$40.41	$40.40	$40.40
Purchase #6	$38.50	5.755%	$40.7157	$40.72	$40.70	$40.70
Purchase #7	$83.94	13.140%	$94.9697	$94.97	$94.95	$95.00
7 purchase totals =	$651.28		$706.9179	$706.92	$706.85	$706.90