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	$127.53	3.130%	$131.5217	$131.52	$131.50	$131.50
Purchase #2	$138.39	7.323%	$148.5243	$148.52	$148.50	$148.50
Purchase #3	$69.87	6.760%	$74.5932	$74.59	$74.60	$74.60
Purchase #4	$28.53	13.494%	$32.3798	$32.38	$32.40	$32.40
Purchase #5	$39.79	5.868%	$42.1249	$42.12	$42.10	$42.10
Purchase #6	$169.93	3.757%	$176.3143	$176.31	$176.30	$176.30
Purchase #7	$179.60	13.795%	$204.3758	$204.38	$204.40	$204.40
7 purchase totals =	$753.64		$809.8340	$809.82	$809.80	$809.80