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	$146.51	12.676%	$165.0816	$165.08	$165.10	$165.10
Purchase #2	$245.98	7.684%	$264.8811	$264.88	$264.90	$264.90
Purchase #3	$185.82	7.612%	$199.9646	$199.96	$199.95	$200.00
Purchase #4	$234.96	3.321%	$242.763	$242.76	$242.75	$242.80
Purchase #5	$107.41	3.852%	$111.5474	$111.55	$111.55	$111.50
Purchase #6	$222.79	6.578%	$237.4451	$237.45	$237.45	$237.40
Purchase #7	$113.76	12.326%	$127.7821	$127.78	$127.80	$127.80
7 purchase totals =	$1,257.23		$1,349.4649	$1,349.46	$1,349.50	$1,349.50