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	$79.42	8.639%	$86.2811	$86.28	$86.30	$86.30
Purchase #2	$35.30	6.466%	$37.5825	$37.58	$37.60	$37.60
Purchase #3	$49.46	12.513%	$55.6489	$55.65	$55.65	$55.60
Purchase #4	$130.66	7.270%	$140.159	$140.16	$140.15	$140.20
Purchase #5	$102.96	8.640%	$111.8557	$111.86	$111.85	$111.90
Purchase #6	$232.94	12.105%	$261.1374	$261.14	$261.15	$261.10
Purchase #7	$158.91	10.685%	$175.8895	$175.89	$175.90	$175.90
7 purchase totals =	$789.65		$868.5541	$868.56	$868.60	$868.60