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	$171.80	6.295%	$182.6148	$182.61	$182.60	$182.60
Purchase #2	$112.75	13.442%	$127.9059	$127.91	$127.90	$127.90
Purchase #3	$173.40	8.215%	$187.6448	$187.64	$187.65	$187.60
Purchase #4	$178.47	3.505%	$184.7254	$184.73	$184.75	$184.70
Purchase #5	$248.26	8.821%	$270.159	$270.16	$270.15	$270.20
Purchase #6	$31.37	13.505%	$35.6065	$35.61	$35.60	$35.60
Purchase #7	$137.71	12.522%	$154.954	$154.95	$154.95	$155.00
7 purchase totals =	$1,053.76		$1,143.6104	$1,143.61	$1,143.60	$1,143.60