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	$90.54	9.135%	$98.8108	$98.81	$98.80	$98.80
Purchase #2	$39.81	13.446%	$45.1629	$45.16	$45.15	$45.20
Purchase #3	$42.27	13.146%	$47.8268	$47.83	$47.85	$47.80
Purchase #4	$21.83	13.368%	$24.7482	$24.75	$24.75	$24.70
Purchase #5	$43.91	9.653%	$48.1486	$48.15	$48.15	$48.10
Purchase #6	$88.34	13.654%	$100.4019	$100.40	$100.40	$100.40
Purchase #7	$41.56	10.587%	$45.96	$45.96	$45.95	$46.00
7 purchase totals =	$368.26		$411.0592	$411.06	$411.05	$411.00