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	$94.82	4.848%	$99.4169	$99.42	$99.40	$99.40
Purchase #2	$223.71	12.523%	$251.7252	$251.73	$251.75	$251.70
Purchase #3	$200.96	13.107%	$227.2998	$227.30	$227.30	$227.30
Purchase #4	$110.43	9.678%	$121.1174	$121.12	$121.10	$121.10
Purchase #5	$250.64	13.651%	$284.8549	$284.85	$284.85	$284.90
Purchase #6	$45.90	9.465%	$50.2444	$50.24	$50.25	$50.20
Purchase #7	$64.96	12.222%	$72.8994	$72.90	$72.90	$72.90
7 purchase totals =	$991.42		$1,107.5580	$1,107.56	$1,107.55	$1,107.50