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	$97.31	11.545%	$108.5444	$108.54	$108.55	$108.50
Purchase #2	$46.96	10.751%	$52.0087	$52.01	$52.00	$52.00
Purchase #3	$85.90	6.326%	$91.334	$91.33	$91.35	$91.30
Purchase #4	$79.53	7.333%	$85.3619	$85.36	$85.35	$85.40
Purchase #5	$12.36	11.519%	$13.7837	$13.78	$13.80	$13.80
Purchase #6	$99.56	5.806%	$105.3405	$105.34	$105.35	$105.30
Purchase #7	$126.83	12.763%	$143.0173	$143.02	$143.00	$143.00
7 purchase totals =	$548.45		$599.3905	$599.38	$599.40	$599.30