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	$242.44	6.553%	$258.3271	$258.33	$258.35	$258.30
Purchase #2	$174.72	13.446%	$198.2129	$198.21	$198.20	$198.20
Purchase #3	$52.96	4.135%	$55.1499	$55.15	$55.15	$55.10
Purchase #4	$119.70	3.444%	$123.8225	$123.82	$123.80	$123.80
Purchase #5	$113.75	12.153%	$127.574	$127.57	$127.55	$127.60
Purchase #6	$128.52	13.342%	$145.6671	$145.67	$145.65	$145.70
Purchase #7	$157.66	7.653%	$169.7257	$169.73	$169.75	$169.70
7 purchase totals =	$989.75		$1,078.4792	$1,078.48	$1,078.45	$1,078.40