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	$127.39	8.113%	$137.7252	$137.73	$137.75	$137.70
Purchase #2	$136.50	4.214%	$142.2521	$142.25	$142.25	$142.30
Purchase #3	$18.68	11.833%	$20.8904	$20.89	$20.90	$20.90
Purchase #4	$97.62	6.496%	$103.9614	$103.96	$103.95	$104.00
Purchase #5	$172.28	11.555%	$192.187	$192.19	$192.20	$192.20
Purchase #6	$50.93	11.485%	$56.7793	$56.78	$56.80	$56.80
Purchase #7	$123.60	6.111%	$131.1532	$131.15	$131.15	$131.20
7 purchase totals =	$727.00		$784.9486	$784.95	$785.00	$785.10