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	$77.85	6.358%	$82.7997	$82.80	$82.80	$82.80
Purchase #2	$87.28	3.348%	$90.2021	$90.20	$90.20	$90.20
Purchase #3	$183.96	4.333%	$191.931	$191.93	$191.95	$191.90
Purchase #4	$69.27	5.178%	$72.8568	$72.86	$72.85	$72.90
Purchase #5	$51.83	3.463%	$53.6249	$53.62	$53.60	$53.60
Purchase #6	$25.72	9.360%	$28.1274	$28.13	$28.15	$28.10
Purchase #7	$241.34	13.625%	$274.2226	$274.22	$274.20	$274.20
7 purchase totals =	$737.25		$793.7645	$793.76	$793.75	$793.70