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	$39.45	7.720%	$42.4955	$42.50	$42.50	$42.50
Purchase #2	$95.47	5.259%	$100.4908	$100.49	$100.50	$100.50
Purchase #3	$165.45	4.514%	$172.9184	$172.92	$172.90	$172.90
Purchase #4	$222.79	11.637%	$248.7161	$248.72	$248.70	$248.70
Purchase #5	$87.30	5.732%	$92.304	$92.30	$92.30	$92.30
Purchase #6	$234.82	6.397%	$249.8414	$249.84	$249.85	$249.80
Purchase #7	$109.38	8.459%	$118.6325	$118.63	$118.65	$118.60
7 purchase totals =	$954.66		$1,025.3987	$1,025.40	$1,025.40	$1,025.30