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	$204.99	9.244%	$223.9393	$223.94	$223.95	$223.90
Purchase #2	$109.31	13.873%	$124.4746	$124.47	$124.45	$124.50
Purchase #3	$46.75	8.829%	$50.8776	$50.88	$50.90	$50.90
Purchase #4	$137.50	5.308%	$144.7985	$144.80	$144.80	$144.80
Purchase #5	$138.96	4.553%	$145.2868	$145.29	$145.30	$145.30
Purchase #6	$92.56	11.408%	$103.1192	$103.12	$103.10	$103.10
Purchase #7	$220.54	7.671%	$237.4576	$237.46	$237.45	$237.50
7 purchase totals =	$950.61		$1,029.9536	$1,029.96	$1,029.95	$1,030.00