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	$14.52	9.614%	$15.916	$15.92	$15.90	$15.90
Purchase #2	$233.95	6.866%	$250.013	$250.01	$250.00	$250.00
Purchase #3	$155.56	6.223%	$165.2405	$165.24	$165.25	$165.20
Purchase #4	$211.81	11.311%	$235.7678	$235.77	$235.75	$235.80
Purchase #5	$80.43	13.279%	$91.1103	$91.11	$91.10	$91.10
Purchase #6	$114.27	11.244%	$127.1185	$127.12	$127.10	$127.10
Purchase #7	$193.93	8.803%	$211.0017	$211.00	$211.00	$211.00
7 purchase totals =	$1,004.47		$1,096.1678	$1,096.17	$1,096.10	$1,096.10