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	$8.97	4.408%	$9.3654	$9.37	$9.35	$9.40
Purchase #2	$89.39	11.753%	$99.896	$99.90	$99.90	$99.90
Purchase #3	$90.49	5.310%	$95.295	$95.30	$95.30	$95.30
Purchase #4	$96.66	6.617%	$103.056	$103.06	$103.05	$103.10
Purchase #5	$212.46	8.382%	$230.2684	$230.27	$230.25	$230.30
Purchase #6	$144.75	8.161%	$156.563	$156.56	$156.55	$156.60
Purchase #7	$113.46	8.700%	$123.331	$123.33	$123.35	$123.30
7 purchase totals =	$756.18		$817.7748	$817.79	$817.75	$817.90