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	$249.69	11.831%	$279.2308	$279.23	$279.25	$279.20
Purchase #2	$222.60	4.400%	$232.3944	$232.39	$232.40	$232.40
Purchase #3	$53.40	10.701%	$59.1143	$59.11	$59.10	$59.10
Purchase #4	$118.75	8.210%	$128.4994	$128.50	$128.50	$128.50
Purchase #5	$77.71	13.147%	$87.9265	$87.93	$87.95	$87.90
Purchase #6	$57.31	6.709%	$61.1549	$61.15	$61.15	$61.20
Purchase #7	$209.30	9.177%	$228.5075	$228.51	$228.50	$228.50
7 purchase totals =	$988.76		$1,076.8278	$1,076.82	$1,076.85	$1,076.80