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	$52.60	7.439%	$56.5129	$56.51	$56.50	$56.50
Purchase #2	$230.29	12.855%	$259.8938	$259.89	$259.90	$259.90
Purchase #3	$70.42	8.278%	$76.2494	$76.25	$76.25	$76.20
Purchase #4	$211.26	6.156%	$224.2652	$224.27	$224.25	$224.30
Purchase #5	$43.71	6.467%	$46.5367	$46.54	$46.55	$46.50
Purchase #6	$123.32	10.290%	$136.0096	$136.01	$136.00	$136.00
Purchase #7	$32.40	8.480%	$35.1475	$35.15	$35.15	$35.10
7 purchase totals =	$764.00		$834.6151	$834.62	$834.60	$834.50