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	$119.98	6.202%	$127.4212	$127.42	$127.40	$127.40
Purchase #2	$55.79	9.453%	$61.0638	$61.06	$61.05	$61.10
Purchase #3	$83.48	10.304%	$92.0818	$92.08	$92.10	$92.10
Purchase #4	$235.68	7.723%	$253.8816	$253.88	$253.90	$253.90
Purchase #5	$238.54	11.769%	$266.6138	$266.61	$266.60	$266.60
Purchase #6	$79.47	9.257%	$86.8265	$86.83	$86.85	$86.80
Purchase #7	$86.58	10.821%	$95.9488	$95.95	$95.95	$95.90
7 purchase totals =	$899.52		$983.8375	$983.83	$983.85	$983.80