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	$80.71	7.511%	$86.7721	$86.77	$86.75	$86.80
Purchase #2	$201.87	10.457%	$222.9795	$222.98	$223.00	$223.00
Purchase #3	$131.34	4.773%	$137.6089	$137.61	$137.60	$137.60
Purchase #4	$146.63	3.831%	$152.2474	$152.25	$152.25	$152.20
Purchase #5	$142.85	5.599%	$150.8482	$150.85	$150.85	$150.80
Purchase #6	$16.85	5.314%	$17.7454	$17.75	$17.75	$17.70
Purchase #7	$77.72	7.768%	$83.7573	$83.76	$83.75	$83.80
7 purchase totals =	$797.97		$851.9588	$851.97	$851.95	$851.90