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	$144.82	9.788%	$158.995	$159.00	$159.00	$159.00
Purchase #2	$31.86	11.553%	$35.5408	$35.54	$35.55	$35.50
Purchase #3	$141.98	7.443%	$152.5476	$152.55	$152.55	$152.50
Purchase #4	$187.80	4.458%	$196.1721	$196.17	$196.15	$196.20
Purchase #5	$147.89	7.345%	$158.7525	$158.75	$158.75	$158.80
Purchase #6	$144.42	4.312%	$150.6474	$150.65	$150.65	$150.60
Purchase #7	$82.27	4.620%	$86.0709	$86.07	$86.05	$86.10
7 purchase totals =	$881.04		$938.7263	$938.73	$938.70	$938.70