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	$90.90	9.846%	$99.85	$99.85	$99.85	$99.90
Purchase #2	$96.66	13.855%	$110.0522	$110.05	$110.05	$110.10
Purchase #3	$244.80	3.396%	$253.1134	$253.11	$253.10	$253.10
Purchase #4	$65.26	3.490%	$67.5376	$67.54	$67.55	$67.50
Purchase #5	$108.71	5.748%	$114.9587	$114.96	$114.95	$115.00
Purchase #6	$28.46	3.523%	$29.4626	$29.46	$29.45	$29.50
Purchase #7	$103.96	13.322%	$117.8096	$117.81	$117.80	$117.80
7 purchase totals =	$738.75		$792.7841	$792.78	$792.75	$792.90