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	$33.39	6.379%	$35.5199	$35.52	$35.50	$35.50
Purchase #2	$222.86	9.631%	$244.3236	$244.32	$244.30	$244.30
Purchase #3	$212.74	10.223%	$234.4884	$234.49	$234.50	$234.50
Purchase #4	$132.55	13.361%	$150.26	$150.26	$150.25	$150.30
Purchase #5	$226.94	11.806%	$253.7325	$253.73	$253.75	$253.70
Purchase #6	$12.25	13.433%	$13.8955	$13.90	$13.90	$13.90
Purchase #7	$202.43	9.783%	$222.2337	$222.23	$222.25	$222.20
7 purchase totals =	$1,043.16		$1,154.4536	$1,154.45	$1,154.45	$1,154.40