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	$217.39	12.318%	$244.1681	$244.17	$244.15	$244.20
Purchase #2	$97.57	8.399%	$105.7649	$105.76	$105.75	$105.80
Purchase #3	$104.27	6.588%	$111.1393	$111.14	$111.15	$111.10
Purchase #4	$63.30	4.794%	$66.3346	$66.33	$66.35	$66.30
Purchase #5	$96.35	3.360%	$99.5874	$99.59	$99.60	$99.60
Purchase #6	$106.95	7.703%	$115.1884	$115.19	$115.20	$115.20
Purchase #7	$103.37	9.328%	$113.0124	$113.01	$113.00	$113.00
7 purchase totals =	$789.20		$855.1951	$855.19	$855.20	$855.20