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	$244.69	13.572%	$277.8993	$277.90	$277.90	$277.90
Purchase #2	$197.30	5.363%	$207.8812	$207.88	$207.90	$207.90
Purchase #3	$95.65	4.666%	$100.113	$100.11	$100.10	$100.10
Purchase #4	$52.31	13.709%	$59.4812	$59.48	$59.50	$59.50
Purchase #5	$56.76	10.671%	$62.8169	$62.82	$62.80	$62.80
Purchase #6	$175.99	13.681%	$200.0672	$200.07	$200.05	$200.10
Purchase #7	$75.69	6.814%	$80.8475	$80.85	$80.85	$80.80
7 purchase totals =	$898.39		$989.1063	$989.11	$989.10	$989.10