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	$105.64	13.574%	$119.9796	$119.98	$120.00	$120.00
Purchase #2	$238.51	7.463%	$256.31	$256.31	$256.30	$256.30
Purchase #3	$199.83	11.618%	$223.0462	$223.05	$223.05	$223.00
Purchase #4	$48.29	3.360%	$49.9125	$49.91	$49.90	$49.90
Purchase #5	$29.77	7.495%	$32.0013	$32.00	$32.00	$32.00
Purchase #6	$133.89	13.348%	$151.7616	$151.76	$151.75	$151.80
Purchase #7	$148.49	8.378%	$160.9305	$160.93	$160.95	$160.90
7 purchase totals =	$904.42		$993.9417	$993.94	$993.95	$993.90