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	$121.61	4.859%	$127.519	$127.52	$127.50	$127.50
Purchase #2	$128.73	10.702%	$142.5067	$142.51	$142.50	$142.50
Purchase #3	$144.76	7.657%	$155.8443	$155.84	$155.85	$155.80
Purchase #4	$46.71	10.127%	$51.4403	$51.44	$51.45	$51.40
Purchase #5	$50.48	11.378%	$56.2236	$56.22	$56.20	$56.20
Purchase #6	$162.78	4.421%	$169.9765	$169.98	$170.00	$170.00
Purchase #7	$88.86	4.555%	$92.9076	$92.91	$92.90	$92.90
7 purchase totals =	$743.93		$796.4180	$796.42	$796.40	$796.30