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	$231.25	8.167%	$250.1362	$250.14	$250.15	$250.10
Purchase #2	$153.75	4.250%	$160.2844	$160.28	$160.30	$160.30
Purchase #3	$140.50	11.464%	$156.6069	$156.61	$156.60	$156.60
Purchase #4	$75.83	8.758%	$82.4712	$82.47	$82.45	$82.50
Purchase #5	$18.73	10.815%	$20.7556	$20.76	$20.75	$20.80
Purchase #6	$190.28	10.496%	$210.2518	$210.25	$210.25	$210.30
Purchase #7	$133.43	11.833%	$149.2188	$149.22	$149.20	$149.20
7 purchase totals =	$943.77		$1,029.7249	$1,029.73	$1,029.70	$1,029.80