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	$176.97	5.345%	$186.429	$186.43	$186.45	$186.40
Purchase #2	$141.54	3.788%	$146.9015	$146.90	$146.90	$146.90
Purchase #3	$175.37	4.318%	$182.9425	$182.94	$182.95	$182.90
Purchase #4	$78.37	8.790%	$85.2587	$85.26	$85.25	$85.30
Purchase #5	$139.49	9.526%	$152.7778	$152.78	$152.80	$152.80
Purchase #6	$66.81	11.640%	$74.5867	$74.59	$74.60	$74.60
Purchase #7	$25.35	9.518%	$27.7628	$27.76	$27.75	$27.80
7 purchase totals =	$803.90		$856.6590	$856.66	$856.70	$856.70