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	$20.73	5.535%	$21.8774	$21.88	$21.90	$21.90
Purchase #2	$45.78	13.669%	$52.0377	$52.04	$52.05	$52.00
Purchase #3	$239.59	11.596%	$267.3729	$267.37	$267.35	$267.40
Purchase #4	$185.29	3.779%	$192.2921	$192.29	$192.30	$192.30
Purchase #5	$236.53	6.465%	$251.8217	$251.82	$251.80	$251.80
Purchase #6	$192.59	6.513%	$205.1334	$205.13	$205.15	$205.10
Purchase #7	$18.42	7.840%	$19.8641	$19.86	$19.85	$19.90
7 purchase totals =	$938.93		$1,010.3993	$1,010.39	$1,010.40	$1,010.40