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	$207.99	10.173%	$229.1488	$229.15	$229.15	$229.10
Purchase #2	$129.59	8.706%	$140.8721	$140.87	$140.85	$140.90
Purchase #3	$57.50	6.683%	$61.3427	$61.34	$61.35	$61.30
Purchase #4	$245.82	13.665%	$279.4113	$279.41	$279.40	$279.40
Purchase #5	$217.64	4.323%	$227.0486	$227.05	$227.05	$227.00
Purchase #6	$165.43	7.837%	$178.3947	$178.39	$178.40	$178.40
Purchase #7	$53.88	3.814%	$55.935	$55.94	$55.95	$55.90
7 purchase totals =	$1,077.85		$1,172.1532	$1,172.15	$1,172.15	$1,172.00