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	$44.34	12.284%	$49.7867	$49.79	$49.80	$49.80
Purchase #2	$175.73	5.633%	$185.6289	$185.63	$185.65	$185.60
Purchase #3	$244.54	8.301%	$264.8393	$264.84	$264.85	$264.80
Purchase #4	$41.68	9.334%	$45.5704	$45.57	$45.55	$45.60
Purchase #5	$116.43	4.457%	$121.6193	$121.62	$121.60	$121.60
Purchase #6	$34.27	10.197%	$37.7645	$37.76	$37.75	$37.80
Purchase #7	$239.40	11.265%	$266.3684	$266.37	$266.35	$266.40
7 purchase totals =	$896.39		$971.5775	$971.58	$971.55	$971.60