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	$153.49	4.244%	$160.0041	$160.00	$160.00	$160.00
Purchase #2	$199.89	3.640%	$207.166	$207.17	$207.15	$207.20
Purchase #3	$46.25	9.595%	$50.6877	$50.69	$50.70	$50.70
Purchase #4	$78.61	13.284%	$89.0526	$89.05	$89.05	$89.10
Purchase #5	$92.39	7.466%	$99.2878	$99.29	$99.30	$99.30
Purchase #6	$215.35	3.669%	$223.2512	$223.25	$223.25	$223.30
Purchase #7	$218.61	8.494%	$237.1787	$237.18	$237.20	$237.20
7 purchase totals =	$1,004.59		$1,066.6281	$1,066.63	$1,066.65	$1,066.80