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	$200.39	6.463%	$213.3412	$213.34	$213.35	$213.30
Purchase #2	$36.85	3.520%	$38.1471	$38.15	$38.15	$38.10
Purchase #3	$89.67	11.127%	$99.6476	$99.65	$99.65	$99.60
Purchase #4	$137.38	5.446%	$144.8617	$144.86	$144.85	$144.90
Purchase #5	$53.25	4.370%	$55.577	$55.58	$55.60	$55.60
Purchase #6	$22.63	13.315%	$25.6432	$25.64	$25.65	$25.60
Purchase #7	$30.80	8.433%	$33.3974	$33.40	$33.40	$33.40
7 purchase totals =	$570.97		$610.6152	$610.62	$610.65	$610.50