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	$52.48	3.423%	$54.2764	$54.28	$54.30	$54.30
Purchase #2	$186.28	5.617%	$196.7433	$196.74	$196.75	$196.70
Purchase #3	$137.98	9.279%	$150.7832	$150.78	$150.80	$150.80
Purchase #4	$250.37	11.776%	$279.8536	$279.85	$279.85	$279.90
Purchase #5	$45.85	10.426%	$50.6303	$50.63	$50.65	$50.60
Purchase #6	$76.86	9.746%	$84.3508	$84.35	$84.35	$84.40
Purchase #7	$133.73	9.350%	$146.2338	$146.23	$146.25	$146.20
7 purchase totals =	$883.55		$962.8714	$962.86	$962.95	$962.90