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	$81.25	11.707%	$90.7619	$90.76	$90.75	$90.80
Purchase #2	$180.49	11.289%	$200.8655	$200.87	$200.85	$200.90
Purchase #3	$33.59	11.553%	$37.4707	$37.47	$37.45	$37.50
Purchase #4	$234.51	7.374%	$251.8028	$251.80	$251.80	$251.80
Purchase #5	$81.75	11.502%	$91.1529	$91.15	$91.15	$91.20
Purchase #6	$217.66	9.298%	$237.898	$237.90	$237.90	$237.90
Purchase #7	$99.33	8.618%	$107.8903	$107.89	$107.90	$107.90
7 purchase totals =	$928.58		$1,017.8421	$1,017.84	$1,017.80	$1,018.00