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	$247.87	13.527%	$281.3994	$281.40	$281.40	$281.40
Purchase #2	$179.48	9.679%	$196.8519	$196.85	$196.85	$196.90
Purchase #3	$206.32	13.208%	$233.5707	$233.57	$233.55	$233.60
Purchase #4	$159.98	10.486%	$176.7555	$176.76	$176.75	$176.80
Purchase #5	$143.62	5.354%	$151.3094	$151.31	$151.30	$151.30
Purchase #6	$39.86	3.107%	$41.0985	$41.10	$41.10	$41.10
Purchase #7	$58.56	6.415%	$62.3166	$62.32	$62.30	$62.30
7 purchase totals =	$1,035.69		$1,143.3020	$1,143.31	$1,143.25	$1,143.40