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	$180.64	4.818%	$189.3432	$189.34	$189.35	$189.30
Purchase #2	$83.44	13.637%	$94.8187	$94.82	$94.80	$94.80
Purchase #3	$226.40	8.281%	$245.1482	$245.15	$245.15	$245.10
Purchase #4	$230.57	10.663%	$255.1557	$255.16	$255.15	$255.20
Purchase #5	$104.43	4.747%	$109.3873	$109.39	$109.40	$109.40
Purchase #6	$45.42	9.266%	$49.6286	$49.63	$49.65	$49.60
Purchase #7	$123.54	11.664%	$137.9497	$137.95	$137.95	$137.90
7 purchase totals =	$994.44		$1,081.4314	$1,081.44	$1,081.45	$1,081.30