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	$80.38	12.767%	$90.6421	$90.64	$90.65	$90.60
Purchase #2	$45.76	12.578%	$51.5157	$51.52	$51.50	$51.50
Purchase #3	$176.75	7.154%	$189.3947	$189.39	$189.40	$189.40
Purchase #4	$150.40	7.792%	$162.1192	$162.12	$162.10	$162.10
Purchase #5	$22.54	6.583%	$24.0238	$24.02	$24.00	$24.00
Purchase #6	$21.73	8.201%	$23.5121	$23.51	$23.50	$23.50
Purchase #7	$74.63	4.874%	$78.2675	$78.27	$78.25	$78.30
7 purchase totals =	$572.19		$619.4751	$619.47	$619.40	$619.40