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	$157.53	9.758%	$172.9018	$172.90	$172.90	$172.90
Purchase #2	$96.78	13.525%	$109.8695	$109.87	$109.85	$109.90
Purchase #3	$9.76	4.394%	$10.1889	$10.19	$10.20	$10.20
Purchase #4	$91.37	8.230%	$98.8898	$98.89	$98.90	$98.90
Purchase #5	$44.42	5.842%	$47.015	$47.02	$47.00	$47.00
Purchase #6	$59.68	3.390%	$61.7032	$61.70	$61.70	$61.70
Purchase #7	$47.80	11.477%	$53.286	$53.29	$53.30	$53.30
7 purchase totals =	$507.34		$553.8542	$553.86	$553.85	$553.90