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	$204.80	6.866%	$218.8616	$218.86	$218.85	$218.90
Purchase #2	$42.92	12.775%	$48.403	$48.40	$48.40	$48.40
Purchase #3	$74.73	4.355%	$77.9845	$77.98	$78.00	$78.00
Purchase #4	$86.59	4.419%	$90.4164	$90.42	$90.40	$90.40
Purchase #5	$212.50	11.579%	$237.1054	$237.11	$237.10	$237.10
Purchase #6	$94.71	8.397%	$102.6628	$102.66	$102.65	$102.70
Purchase #7	$119.61	6.418%	$127.2866	$127.29	$127.30	$127.30
7 purchase totals =	$835.86		$902.7203	$902.72	$902.70	$902.80