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	$143.46	3.269%	$148.1497	$148.15	$148.15	$148.10
Purchase #2	$45.27	9.161%	$49.4172	$49.42	$49.40	$49.40
Purchase #3	$70.36	11.597%	$78.5196	$78.52	$78.50	$78.50
Purchase #4	$130.48	9.683%	$143.1144	$143.11	$143.10	$143.10
Purchase #5	$152.50	5.149%	$160.3522	$160.35	$160.35	$160.40
Purchase #6	$179.93	10.331%	$198.5186	$198.52	$198.50	$198.50
Purchase #7	$95.96	7.801%	$103.4458	$103.45	$103.45	$103.40
7 purchase totals =	$817.96		$881.5175	$881.52	$881.45	$881.40