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	$213.77	11.461%	$238.2702	$238.27	$238.25	$238.30
Purchase #2	$133.71	7.421%	$143.6326	$143.63	$143.65	$143.60
Purchase #3	$124.51	9.872%	$136.8016	$136.80	$136.80	$136.80
Purchase #4	$187.95	6.735%	$200.6084	$200.61	$200.60	$200.60
Purchase #5	$45.72	10.742%	$50.6312	$50.63	$50.65	$50.60
Purchase #6	$50.78	3.499%	$52.5568	$52.56	$52.55	$52.60
Purchase #7	$172.81	3.679%	$179.1677	$179.17	$179.15	$179.20
7 purchase totals =	$929.25		$1,001.6685	$1,001.67	$1,001.65	$1,001.70