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	$123.82	3.617%	$128.2986	$128.30	$128.30	$128.30
Purchase #2	$208.29	9.534%	$228.1484	$228.15	$228.15	$228.10
Purchase #3	$157.70	10.548%	$174.3342	$174.33	$174.35	$174.30
Purchase #4	$81.29	11.635%	$90.7481	$90.75	$90.75	$90.70
Purchase #5	$239.84	4.304%	$250.1627	$250.16	$250.15	$250.20
Purchase #6	$129.28	13.523%	$146.7625	$146.76	$146.75	$146.80
Purchase #7	$7.25	6.647%	$7.7319	$7.73	$7.75	$7.70
7 purchase totals =	$947.47		$1,026.1864	$1,026.18	$1,026.20	$1,026.10