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	$26.53	6.470%	$28.2465	$28.25	$28.25	$28.20
Purchase #2	$89.69	5.464%	$94.5907	$94.59	$94.60	$94.60
Purchase #3	$242.29	11.786%	$270.8463	$270.85	$270.85	$270.80
Purchase #4	$32.76	4.483%	$34.2286	$34.23	$34.25	$34.20
Purchase #5	$161.50	13.267%	$182.9262	$182.93	$182.95	$182.90
Purchase #6	$165.66	4.733%	$173.5007	$173.50	$173.50	$173.50
Purchase #7	$196.28	10.123%	$216.1494	$216.15	$216.15	$216.10
7 purchase totals =	$914.71		$1,000.4884	$1,000.50	$1,000.55	$1,000.30