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	$99.53	3.843%	$103.3549	$103.35	$103.35	$103.40
Purchase #2	$246.43	4.689%	$257.9851	$257.99	$258.00	$258.00
Purchase #3	$66.70	7.478%	$71.6878	$71.69	$71.70	$71.70
Purchase #4	$24.97	8.681%	$27.1376	$27.14	$27.15	$27.10
Purchase #5	$179.28	9.506%	$196.3224	$196.32	$196.30	$196.30
Purchase #6	$12.63	6.670%	$13.4724	$13.47	$13.45	$13.50
Purchase #7	$217.35	12.235%	$243.9428	$243.94	$243.95	$243.90
7 purchase totals =	$846.89		$913.9030	$913.90	$913.90	$913.90