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	$122.52	7.426%	$131.6183	$131.62	$131.60	$131.60
Purchase #2	$226.37	3.288%	$233.813	$233.81	$233.80	$233.80
Purchase #3	$34.98	4.531%	$36.5649	$36.56	$36.55	$36.60
Purchase #4	$105.28	6.589%	$112.2169	$112.22	$112.20	$112.20
Purchase #5	$72.44	13.858%	$82.4787	$82.48	$82.50	$82.50
Purchase #6	$121.62	10.107%	$133.9121	$133.91	$133.90	$133.90
Purchase #7	$67.51	11.786%	$75.4667	$75.47	$75.45	$75.50
7 purchase totals =	$750.72		$806.0706	$806.07	$806.00	$806.10