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	$195.60	6.640%	$208.5878	$208.59	$208.60	$208.60
Purchase #2	$106.78	12.382%	$120.0015	$120.00	$120.00	$120.00
Purchase #3	$223.29	3.832%	$231.8465	$231.85	$231.85	$231.80
Purchase #4	$54.44	3.408%	$56.2953	$56.30	$56.30	$56.30
Purchase #5	$154.77	6.715%	$165.1628	$165.16	$165.15	$165.20
Purchase #6	$197.30	5.412%	$207.9779	$207.98	$208.00	$208.00
Purchase #7	$84.57	7.275%	$90.7225	$90.72	$90.70	$90.70
7 purchase totals =	$1,016.75		$1,080.5943	$1,080.60	$1,080.60	$1,080.60