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	$204.89	11.817%	$229.1019	$229.10	$229.10	$229.10
Purchase #2	$250.46	7.686%	$269.7104	$269.71	$269.70	$269.70
Purchase #3	$58.51	6.415%	$62.2634	$62.26	$62.25	$62.30
Purchase #4	$23.64	9.620%	$25.9142	$25.91	$25.90	$25.90
Purchase #5	$37.84	6.706%	$40.3776	$40.38	$40.40	$40.40
Purchase #6	$96.85	3.104%	$99.8562	$99.86	$99.85	$99.90
Purchase #7	$132.50	5.367%	$139.6113	$139.61	$139.60	$139.60
7 purchase totals =	$804.69		$866.8350	$866.83	$866.80	$866.90