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	$153.45	8.335%	$166.2401	$166.24	$166.25	$166.20
Purchase #2	$119.44	9.628%	$130.9397	$130.94	$130.95	$130.90
Purchase #3	$34.73	13.781%	$39.5161	$39.52	$39.50	$39.50
Purchase #4	$138.67	8.689%	$150.719	$150.72	$150.70	$150.70
Purchase #5	$127.90	8.155%	$138.3302	$138.33	$138.35	$138.30
Purchase #6	$182.83	3.185%	$188.6531	$188.65	$188.65	$188.70
Purchase #7	$81.45	9.667%	$89.3238	$89.32	$89.30	$89.30
7 purchase totals =	$838.47		$903.7220	$903.72	$903.70	$903.60