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	$18.97	7.785%	$20.4468	$20.45	$20.45	$20.40
Purchase #2	$223.46	12.144%	$250.597	$250.60	$250.60	$250.60
Purchase #3	$199.27	12.175%	$223.5311	$223.53	$223.55	$223.50
Purchase #4	$136.78	4.420%	$142.8257	$142.83	$142.85	$142.80
Purchase #5	$231.50	12.260%	$259.8819	$259.88	$259.90	$259.90
Purchase #6	$113.77	7.476%	$122.2754	$122.28	$122.30	$122.30
Purchase #7	$133.92	13.523%	$152.03	$152.03	$152.05	$152.00
7 purchase totals =	$1,057.67		$1,171.5879	$1,171.60	$1,171.70	$1,171.50