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	$82.59	6.790%	$88.1979	$88.20	$88.20	$88.20
Purchase #2	$123.27	13.448%	$139.8473	$139.85	$139.85	$139.80
Purchase #3	$114.25	4.105%	$118.94	$118.94	$118.95	$118.90
Purchase #4	$221.73	8.618%	$240.8387	$240.84	$240.85	$240.80
Purchase #5	$114.51	3.683%	$118.7274	$118.73	$118.75	$118.70
Purchase #6	$137.96	4.769%	$144.5393	$144.54	$144.55	$144.50
Purchase #7	$51.43	5.331%	$54.1717	$54.17	$54.15	$54.20
7 purchase totals =	$845.74		$905.2623	$905.27	$905.30	$905.10