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	$250.95	13.874%	$285.7668	$285.77	$285.75	$285.80
Purchase #2	$175.98	13.109%	$199.0492	$199.05	$199.05	$199.00
Purchase #3	$42.72	11.637%	$47.6913	$47.69	$47.70	$47.70
Purchase #4	$58.66	4.650%	$61.3877	$61.39	$61.40	$61.40
Purchase #5	$236.85	7.827%	$255.3882	$255.39	$255.40	$255.40
Purchase #6	$133.30	6.460%	$141.9112	$141.91	$141.90	$141.90
Purchase #7	$146.84	5.354%	$154.7018	$154.70	$154.70	$154.70
7 purchase totals =	$1,045.30		$1,145.8962	$1,145.90	$1,145.90	$1,145.90