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	$109.80	4.309%	$114.5313	$114.53	$114.55	$114.50
Purchase #2	$161.57	10.489%	$178.5171	$178.52	$178.50	$178.50
Purchase #3	$103.48	8.344%	$112.1144	$112.11	$112.10	$112.10
Purchase #4	$62.64	3.188%	$64.637	$64.64	$64.65	$64.60
Purchase #5	$213.37	3.640%	$221.1367	$221.14	$221.15	$221.10
Purchase #6	$100.28	5.275%	$105.5698	$105.57	$105.55	$105.60
Purchase #7	$32.45	3.455%	$33.5711	$33.57	$33.55	$33.60
7 purchase totals =	$783.59		$830.0774	$830.08	$830.05	$830.00