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	$74.77	12.178%	$83.8755	$83.88	$83.90	$83.90
Purchase #2	$197.58	12.104%	$221.4951	$221.50	$221.50	$221.50
Purchase #3	$88.86	12.380%	$99.8609	$99.86	$99.85	$99.90
Purchase #4	$207.86	3.740%	$215.634	$215.63	$215.65	$215.60
Purchase #5	$177.84	4.204%	$185.3164	$185.32	$185.30	$185.30
Purchase #6	$116.76	9.225%	$127.5311	$127.53	$127.55	$127.50
Purchase #7	$133.88	4.741%	$140.2273	$140.23	$140.25	$140.20
7 purchase totals =	$997.55		$1,073.9403	$1,073.95	$1,074.00	$1,073.90