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	$166.54	11.481%	$185.6605	$185.66	$185.65	$185.70
Purchase #2	$94.81	10.644%	$104.9016	$104.90	$104.90	$104.90
Purchase #3	$119.98	12.765%	$135.2954	$135.30	$135.30	$135.30
Purchase #4	$60.41	11.132%	$67.1348	$67.13	$67.15	$67.10
Purchase #5	$25.92	10.284%	$28.5856	$28.59	$28.60	$28.60
Purchase #6	$11.91	6.302%	$12.6606	$12.66	$12.65	$12.70
Purchase #7	$91.60	8.751%	$99.6159	$99.62	$99.60	$99.60
7 purchase totals =	$571.17		$633.8544	$633.86	$633.85	$633.90