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	$91.33	13.314%	$103.4897	$103.49	$103.50	$103.50
Purchase #2	$33.76	10.417%	$37.2768	$37.28	$37.30	$37.30
Purchase #3	$142.85	8.613%	$155.1537	$155.15	$155.15	$155.20
Purchase #4	$105.70	3.263%	$109.149	$109.15	$109.15	$109.10
Purchase #5	$216.87	7.405%	$232.9292	$232.93	$232.95	$232.90
Purchase #6	$126.76	8.748%	$137.849	$137.85	$137.85	$137.80
Purchase #7	$236.25	8.298%	$255.854	$255.85	$255.85	$255.90
7 purchase totals =	$953.52		$1,031.7014	$1,031.70	$1,031.75	$1,031.70