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	$242.55	9.791%	$266.2981	$266.30	$266.30	$266.30
Purchase #2	$166.54	4.428%	$173.9144	$173.91	$173.90	$173.90
Purchase #3	$53.30	12.187%	$59.7957	$59.80	$59.80	$59.80
Purchase #4	$87.66	11.865%	$98.0609	$98.06	$98.05	$98.10
Purchase #5	$52.33	10.299%	$57.7195	$57.72	$57.70	$57.70
Purchase #6	$171.42	11.264%	$190.7287	$190.73	$190.75	$190.70
Purchase #7	$185.38	6.325%	$197.1053	$197.11	$197.10	$197.10
7 purchase totals =	$959.18		$1,043.6226	$1,043.63	$1,043.60	$1,043.60