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	$53.90	13.863%	$61.3722	$61.37	$61.35	$61.40
Purchase #2	$99.26	11.379%	$110.5548	$110.55	$110.55	$110.60
Purchase #3	$98.70	13.796%	$112.3167	$112.32	$112.30	$112.30
Purchase #4	$109.60	4.765%	$114.8224	$114.82	$114.80	$114.80
Purchase #5	$142.69	13.582%	$162.0702	$162.07	$162.05	$162.10
Purchase #6	$83.89	7.127%	$89.8688	$89.87	$89.85	$89.90
Purchase #7	$130.37	9.673%	$142.9807	$142.98	$143.00	$143.00
7 purchase totals =	$718.41		$793.9858	$793.98	$793.90	$794.10