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	$77.83	5.639%	$82.2188	$82.22	$82.20	$82.20
Purchase #2	$173.98	3.771%	$180.5408	$180.54	$180.55	$180.50
Purchase #3	$225.72	3.289%	$233.1439	$233.14	$233.15	$233.10
Purchase #4	$121.86	5.341%	$128.3685	$128.37	$128.35	$128.40
Purchase #5	$85.65	5.387%	$90.264	$90.26	$90.25	$90.30
Purchase #6	$75.65	5.174%	$79.5641	$79.56	$79.55	$79.60
Purchase #7	$45.86	5.241%	$48.2635	$48.26	$48.25	$48.30
7 purchase totals =	$806.55		$842.3636	$842.35	$842.30	$842.40