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	$250.63	11.384%	$279.1617	$279.16	$279.15	$279.20
Purchase #2	$183.95	11.333%	$204.7971	$204.80	$204.80	$204.80
Purchase #3	$59.75	4.447%	$62.4071	$62.41	$62.40	$62.40
Purchase #4	$7.46	6.145%	$7.9184	$7.92	$7.90	$7.90
Purchase #5	$233.76	7.390%	$251.0349	$251.03	$251.05	$251.00
Purchase #6	$73.80	5.559%	$77.9025	$77.90	$77.90	$77.90
Purchase #7	$133.38	6.838%	$142.5005	$142.50	$142.50	$142.50
7 purchase totals =	$942.73		$1,025.7222	$1,025.72	$1,025.70	$1,025.70