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	$70.77	11.341%	$78.796	$78.80	$78.80	$78.80
Purchase #2	$167.69	9.413%	$183.4747	$183.47	$183.45	$183.50
Purchase #3	$243.88	4.693%	$255.3253	$255.33	$255.35	$255.30
Purchase #4	$243.98	11.136%	$271.1496	$271.15	$271.15	$271.10
Purchase #5	$164.42	12.721%	$185.3359	$185.34	$185.35	$185.30
Purchase #6	$95.26	11.798%	$106.4988	$106.50	$106.50	$106.50
Purchase #7	$242.99	13.191%	$275.0428	$275.04	$275.05	$275.00
7 purchase totals =	$1,228.99		$1,355.6231	$1,355.63	$1,355.65	$1,355.50