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	$99.62	5.714%	$105.3123	$105.31	$105.30	$105.30
Purchase #2	$5.44	13.370%	$6.1673	$6.17	$6.15	$6.20
Purchase #3	$73.92	11.169%	$82.1761	$82.18	$82.20	$82.20
Purchase #4	$110.69	4.431%	$115.5947	$115.59	$115.60	$115.60
Purchase #5	$135.86	5.326%	$143.0959	$143.10	$143.10	$143.10
Purchase #6	$154.37	4.185%	$160.8304	$160.83	$160.85	$160.80
Purchase #7	$86.31	6.700%	$92.0928	$92.09	$92.10	$92.10
7 purchase totals =	$666.21		$705.2695	$705.27	$705.30	$705.30