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	$28.25	8.602%	$30.6801	$30.68	$30.70	$30.70
Purchase #2	$30.86	3.575%	$31.9632	$31.96	$31.95	$32.00
Purchase #3	$104.71	6.379%	$111.3895	$111.39	$111.40	$111.40
Purchase #4	$40.32	4.515%	$42.1404	$42.14	$42.15	$42.10
Purchase #5	$184.50	3.160%	$190.3302	$190.33	$190.35	$190.30
Purchase #6	$93.53	11.443%	$104.2326	$104.23	$104.25	$104.20
Purchase #7	$17.36	4.506%	$18.1422	$18.14	$18.15	$18.10
7 purchase totals =	$499.53		$528.8782	$528.87	$528.95	$528.80