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	$127.70	12.109%	$143.1632	$143.16	$143.15	$143.20
Purchase #2	$148.96	7.781%	$160.5506	$160.55	$160.55	$160.60
Purchase #3	$248.61	10.285%	$274.1795	$274.18	$274.20	$274.20
Purchase #4	$126.63	11.757%	$141.5179	$141.52	$141.50	$141.50
Purchase #5	$43.29	7.430%	$46.5064	$46.51	$46.50	$46.50
Purchase #6	$165.64	4.269%	$172.7112	$172.71	$172.70	$172.70
Purchase #7	$31.89	8.332%	$34.5471	$34.55	$34.55	$34.50
7 purchase totals =	$892.72		$973.1759	$973.18	$973.15	$973.20