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	$208.27	8.413%	$225.7918	$225.79	$225.80	$225.80
Purchase #2	$164.70	11.205%	$183.1546	$183.15	$183.15	$183.20
Purchase #3	$244.39	6.753%	$260.8937	$260.89	$260.90	$260.90
Purchase #4	$137.79	9.489%	$150.8649	$150.86	$150.85	$150.90
Purchase #5	$151.92	4.689%	$159.0435	$159.04	$159.05	$159.00
Purchase #6	$101.90	9.107%	$111.18	$111.18	$111.20	$111.20
Purchase #7	$173.82	5.822%	$183.9398	$183.94	$183.95	$183.90
7 purchase totals =	$1,182.79		$1,274.8683	$1,274.85	$1,274.90	$1,274.90