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	$88.81	12.156%	$99.6057	$99.61	$99.60	$99.60
Purchase #2	$177.98	12.516%	$200.256	$200.26	$200.25	$200.30
Purchase #3	$134.41	9.790%	$147.5687	$147.57	$147.55	$147.60
Purchase #4	$149.68	4.642%	$156.6281	$156.63	$156.65	$156.60
Purchase #5	$34.39	13.652%	$39.0849	$39.08	$39.10	$39.10
Purchase #6	$29.43	12.655%	$33.1544	$33.15	$33.15	$33.20
Purchase #7	$129.80	9.526%	$142.1647	$142.16	$142.15	$142.20
7 purchase totals =	$744.50		$818.4625	$818.46	$818.45	$818.60