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	$73.26	3.631%	$75.9201	$75.92	$75.90	$75.90
Purchase #2	$51.97	8.685%	$56.4836	$56.48	$56.50	$56.50
Purchase #3	$199.37	11.464%	$222.2258	$222.23	$222.25	$222.20
Purchase #4	$91.97	4.237%	$95.8668	$95.87	$95.85	$95.90
Purchase #5	$91.44	8.871%	$99.5516	$99.55	$99.55	$99.60
Purchase #6	$173.86	13.145%	$196.7139	$196.71	$196.70	$196.70
Purchase #7	$92.42	9.698%	$101.3829	$101.38	$101.40	$101.40
7 purchase totals =	$774.29		$848.1447	$848.14	$848.15	$848.20