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	$88.67	7.406%	$95.2369	$95.24	$95.25	$95.20
Purchase #2	$126.93	11.318%	$141.2959	$141.30	$141.30	$141.30
Purchase #3	$115.48	10.539%	$127.6504	$127.65	$127.65	$127.70
Purchase #4	$104.42	8.820%	$113.6298	$113.63	$113.65	$113.60
Purchase #5	$38.39	10.479%	$42.4129	$42.41	$42.40	$42.40
Purchase #6	$29.27	12.723%	$32.994	$32.99	$33.00	$33.00
Purchase #7	$76.89	11.363%	$85.627	$85.63	$85.65	$85.60
7 purchase totals =	$580.05		$638.8469	$638.85	$638.90	$638.80