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	$70.34	11.641%	$78.5283	$78.53	$78.55	$78.50
Purchase #2	$181.87	6.814%	$194.2626	$194.26	$194.25	$194.30
Purchase #3	$120.60	8.137%	$130.4132	$130.41	$130.40	$130.40
Purchase #4	$160.35	7.661%	$172.6344	$172.63	$172.65	$172.60
Purchase #5	$87.43	12.436%	$98.3028	$98.30	$98.30	$98.30
Purchase #6	$35.57	8.175%	$38.4778	$38.48	$38.50	$38.50
Purchase #7	$184.52	11.384%	$205.5258	$205.53	$205.55	$205.50
7 purchase totals =	$840.68		$918.1449	$918.14	$918.20	$918.10