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	$32.91	8.167%	$35.5978	$35.60	$35.60	$35.60
Purchase #2	$91.93	7.183%	$98.5333	$98.53	$98.55	$98.50
Purchase #3	$116.37	6.421%	$123.8421	$123.84	$123.85	$123.80
Purchase #4	$46.95	10.632%	$51.9417	$51.94	$51.95	$51.90
Purchase #5	$61.50	10.246%	$67.8013	$67.80	$67.80	$67.80
Purchase #6	$79.60	9.102%	$86.8452	$86.85	$86.85	$86.80
Purchase #7	$219.83	3.222%	$226.9129	$226.91	$226.90	$226.90
7 purchase totals =	$649.09		$691.4743	$691.47	$691.50	$691.30