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	$17.79	6.190%	$18.8912	$18.89	$18.90	$18.90
Purchase #2	$131.61	9.625%	$144.2775	$144.28	$144.30	$144.30
Purchase #3	$58.52	5.674%	$61.8404	$61.84	$61.85	$61.80
Purchase #4	$133.41	7.538%	$143.4664	$143.47	$143.45	$143.50
Purchase #5	$186.48	10.715%	$206.4613	$206.46	$206.45	$206.50
Purchase #6	$36.97	13.262%	$41.873	$41.87	$41.85	$41.90
Purchase #7	$43.77	4.177%	$45.5983	$45.60	$45.60	$45.60
7 purchase totals =	$608.55		$662.4081	$662.41	$662.40	$662.50