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	$240.92	7.573%	$259.1649	$259.16	$259.15	$259.20
Purchase #2	$213.56	13.432%	$242.2454	$242.25	$242.25	$242.20
Purchase #3	$54.32	9.139%	$59.2843	$59.28	$59.30	$59.30
Purchase #4	$52.74	12.308%	$59.2312	$59.23	$59.25	$59.20
Purchase #5	$234.38	9.127%	$255.7719	$255.77	$255.75	$255.80
Purchase #6	$155.78	5.409%	$164.2061	$164.21	$164.20	$164.20
Purchase #7	$246.75	5.125%	$259.3959	$259.40	$259.40	$259.40
7 purchase totals =	$1,198.45		$1,299.2997	$1,299.30	$1,299.30	$1,299.30