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	$104.91	6.443%	$111.6694	$111.67	$111.65	$111.70
Purchase #2	$124.80	4.299%	$130.1652	$130.17	$130.15	$130.20
Purchase #3	$129.64	12.180%	$145.4302	$145.43	$145.45	$145.40
Purchase #4	$10.59	3.280%	$10.9374	$10.94	$10.95	$10.90
Purchase #5	$232.78	7.820%	$250.9834	$250.98	$251.00	$251.00
Purchase #6	$84.55	12.271%	$94.9251	$94.93	$94.95	$94.90
Purchase #7	$83.85	10.733%	$92.8496	$92.85	$92.85	$92.80
7 purchase totals =	$771.12		$836.9603	$836.97	$837.00	$836.90