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	$7.79	12.788%	$8.7862	$8.79	$8.80	$8.80
Purchase #2	$106.40	4.632%	$111.3284	$111.33	$111.35	$111.30
Purchase #3	$99.64	12.180%	$111.7762	$111.78	$111.80	$111.80
Purchase #4	$214.48	10.650%	$237.3221	$237.32	$237.30	$237.30
Purchase #5	$36.29	8.126%	$39.2389	$39.24	$39.25	$39.20
Purchase #6	$50.41	7.825%	$54.3546	$54.35	$54.35	$54.40
Purchase #7	$154.74	6.392%	$164.631	$164.63	$164.65	$164.60
7 purchase totals =	$669.75		$727.4374	$727.44	$727.50	$727.40