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	$237.96	13.480%	$270.037	$270.04	$270.05	$270.00
Purchase #2	$107.99	5.372%	$113.7912	$113.79	$113.80	$113.80
Purchase #3	$52.92	12.404%	$59.4842	$59.48	$59.50	$59.50
Purchase #4	$228.53	8.304%	$247.5071	$247.51	$247.50	$247.50
Purchase #5	$165.49	7.852%	$178.4843	$178.48	$178.50	$178.50
Purchase #6	$161.44	7.424%	$173.4253	$173.43	$173.45	$173.40
Purchase #7	$65.45	9.304%	$71.5395	$71.54	$71.55	$71.50
7 purchase totals =	$1,019.78		$1,114.2686	$1,114.27	$1,114.35	$1,114.20