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	$69.35	13.139%	$78.4619	$78.46	$78.45	$78.50
Purchase #2	$73.63	12.704%	$82.984	$82.98	$83.00	$83.00
Purchase #3	$231.86	13.362%	$262.8411	$262.84	$262.85	$262.80
Purchase #4	$165.43	11.861%	$185.0517	$185.05	$185.05	$185.10
Purchase #5	$48.40	11.817%	$54.1194	$54.12	$54.10	$54.10
Purchase #6	$7.52	9.569%	$8.2396	$8.24	$8.25	$8.20
Purchase #7	$106.25	4.847%	$111.3999	$111.40	$111.40	$111.40
7 purchase totals =	$702.44		$783.0976	$783.09	$783.10	$783.10