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	$132.61	7.424%	$142.455	$142.46	$142.45	$142.50
Purchase #2	$170.31	12.349%	$191.3416	$191.34	$191.35	$191.30
Purchase #3	$130.78	5.212%	$137.5963	$137.60	$137.60	$137.60
Purchase #4	$39.59	13.215%	$44.8218	$44.82	$44.80	$44.80
Purchase #5	$108.41	12.761%	$122.2442	$122.24	$122.25	$122.20
Purchase #6	$91.60	9.618%	$100.4101	$100.41	$100.40	$100.40
Purchase #7	$99.65	7.256%	$106.8806	$106.88	$106.90	$106.90
7 purchase totals =	$772.95		$845.7496	$845.75	$845.75	$845.70