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	$161.40	12.490%	$181.5589	$181.56	$181.55	$181.60
Purchase #2	$90.32	12.316%	$101.4438	$101.44	$101.45	$101.40
Purchase #3	$76.63	11.429%	$85.388	$85.39	$85.40	$85.40
Purchase #4	$80.25	7.343%	$86.1428	$86.14	$86.15	$86.10
Purchase #5	$223.46	5.165%	$235.0017	$235.00	$235.00	$235.00
Purchase #6	$85.55	5.302%	$90.0859	$90.09	$90.10	$90.10
Purchase #7	$66.62	7.544%	$71.6458	$71.65	$71.65	$71.60
7 purchase totals =	$784.23		$851.2669	$851.27	$851.30	$851.20