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	$57.87	11.604%	$64.5852	$64.59	$64.60	$64.60
Purchase #2	$175.30	8.845%	$190.8053	$190.81	$190.80	$190.80
Purchase #3	$186.39	13.504%	$211.5601	$211.56	$211.55	$211.60
Purchase #4	$248.61	8.337%	$269.3366	$269.34	$269.35	$269.30
Purchase #5	$42.71	13.125%	$48.3157	$48.32	$48.30	$48.30
Purchase #6	$83.55	9.497%	$91.4847	$91.48	$91.50	$91.50
Purchase #7	$118.60	11.194%	$131.8761	$131.88	$131.90	$131.90
7 purchase totals =	$913.03		$1,007.9637	$1,007.98	$1,008.00	$1,008.00