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	$94.56	4.727%	$99.0299	$99.03	$99.05	$99.00
Purchase #2	$87.29	13.705%	$99.2531	$99.25	$99.25	$99.30
Purchase #3	$219.91	10.215%	$242.3738	$242.37	$242.35	$242.40
Purchase #4	$108.46	10.552%	$119.9047	$119.90	$119.90	$119.90
Purchase #5	$102.46	5.708%	$108.3084	$108.31	$108.30	$108.30
Purchase #6	$78.99	9.349%	$86.3748	$86.37	$86.35	$86.40
Purchase #7	$54.93	13.360%	$62.2686	$62.27	$62.25	$62.30
7 purchase totals =	$746.60		$817.5133	$817.50	$817.45	$817.60