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	$40.45	5.829%	$42.8078	$42.81	$42.80	$42.80
Purchase #2	$75.40	9.596%	$82.6354	$82.64	$82.65	$82.60
Purchase #3	$171.94	9.522%	$188.3121	$188.31	$188.30	$188.30
Purchase #4	$136.27	12.817%	$153.7357	$153.74	$153.75	$153.70
Purchase #5	$137.28	11.821%	$153.5079	$153.51	$153.50	$153.50
Purchase #6	$150.32	13.208%	$170.1743	$170.17	$170.15	$170.20
Purchase #7	$31.36	11.458%	$34.9532	$34.95	$34.95	$35.00
7 purchase totals =	$743.02		$826.1264	$826.13	$826.10	$826.10