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	$20.98	13.830%	$23.8815	$23.88	$23.90	$23.90
Purchase #2	$135.65	11.296%	$150.973	$150.97	$150.95	$151.00
Purchase #3	$175.64	5.643%	$185.5514	$185.55	$185.55	$185.60
Purchase #4	$127.78	3.621%	$132.4069	$132.41	$132.40	$132.40
Purchase #5	$170.85	6.425%	$181.8271	$181.83	$181.85	$181.80
Purchase #6	$228.75	11.428%	$254.8916	$254.89	$254.90	$254.90
Purchase #7	$157.98	6.593%	$168.3956	$168.40	$168.40	$168.40
7 purchase totals =	$1,017.63		$1,097.9271	$1,097.93	$1,097.95	$1,098.00