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	$225.73	12.487%	$253.9169	$253.92	$253.90	$253.90
Purchase #2	$195.89	11.611%	$218.6348	$218.63	$218.65	$218.60
Purchase #3	$47.48	10.424%	$52.4293	$52.43	$52.45	$52.40
Purchase #4	$141.59	8.152%	$153.1324	$153.13	$153.15	$153.10
Purchase #5	$12.98	12.413%	$14.5912	$14.59	$14.60	$14.60
Purchase #6	$191.75	11.524%	$213.8473	$213.85	$213.85	$213.80
Purchase #7	$35.75	13.457%	$40.5609	$40.56	$40.55	$40.60
7 purchase totals =	$851.17		$947.1128	$947.11	$947.15	$947.00