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	$29.50	7.382%	$31.6777	$31.68	$31.70	$31.70
Purchase #2	$198.73	4.575%	$207.8219	$207.82	$207.80	$207.80
Purchase #3	$98.94	8.681%	$107.529	$107.53	$107.55	$107.50
Purchase #4	$90.45	11.118%	$100.5062	$100.51	$100.50	$100.50
Purchase #5	$19.71	11.231%	$21.9236	$21.92	$21.90	$21.90
Purchase #6	$28.57	3.386%	$29.5374	$29.54	$29.55	$29.50
Purchase #7	$108.55	7.304%	$116.4785	$116.48	$116.50	$116.50
7 purchase totals =	$574.45		$615.4743	$615.48	$615.50	$615.40