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	$10.88	12.374%	$12.2263	$12.23	$12.25	$12.20
Purchase #2	$146.70	12.205%	$164.6047	$164.60	$164.60	$164.60
Purchase #3	$30.64	8.180%	$33.1464	$33.15	$33.15	$33.10
Purchase #4	$139.45	8.854%	$151.7969	$151.80	$151.80	$151.80
Purchase #5	$56.70	13.550%	$64.3829	$64.38	$64.40	$64.40
Purchase #6	$65.56	5.107%	$68.9081	$68.91	$68.90	$68.90
Purchase #7	$176.37	11.404%	$196.4832	$196.48	$196.50	$196.50
7 purchase totals =	$626.30		$691.5485	$691.55	$691.60	$691.50