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	$142.84	6.507%	$152.1346	$152.13	$152.15	$152.10
Purchase #2	$90.79	10.685%	$100.4909	$100.49	$100.50	$100.50
Purchase #3	$121.78	8.138%	$131.6905	$131.69	$131.70	$131.70
Purchase #4	$145.72	3.549%	$150.8916	$150.89	$150.90	$150.90
Purchase #5	$41.68	13.324%	$47.2334	$47.23	$47.25	$47.20
Purchase #6	$159.57	7.869%	$172.1266	$172.13	$172.15	$172.10
Purchase #7	$64.29	4.271%	$67.0358	$67.04	$67.05	$67.00
7 purchase totals =	$766.67		$821.6034	$821.60	$821.70	$821.50