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	$119.73	13.426%	$135.8049	$135.80	$135.80	$135.80
Purchase #2	$232.34	5.557%	$245.2511	$245.25	$245.25	$245.30
Purchase #3	$158.61	8.635%	$172.306	$172.31	$172.30	$172.30
Purchase #4	$223.83	12.457%	$251.7125	$251.71	$251.70	$251.70
Purchase #5	$131.48	4.798%	$137.7884	$137.79	$137.80	$137.80
Purchase #6	$161.87	10.796%	$179.3455	$179.35	$179.35	$179.30
Purchase #7	$75.75	3.781%	$78.6141	$78.61	$78.60	$78.60
7 purchase totals =	$1,103.61		$1,200.8225	$1,200.82	$1,200.80	$1,200.80