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	$170.40	6.327%	$181.1812	$181.18	$181.20	$181.20
Purchase #2	$72.93	7.606%	$78.4771	$78.48	$78.50	$78.50
Purchase #3	$206.89	11.628%	$230.9472	$230.95	$230.95	$230.90
Purchase #4	$17.92	5.532%	$18.9113	$18.91	$18.90	$18.90
Purchase #5	$189.39	4.261%	$197.4599	$197.46	$197.45	$197.50
Purchase #6	$37.83	3.400%	$39.1162	$39.12	$39.10	$39.10
Purchase #7	$162.61	10.196%	$179.1897	$179.19	$179.20	$179.20
7 purchase totals =	$857.97		$925.2826	$925.29	$925.30	$925.30