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	$171.94	4.508%	$179.6911	$179.69	$179.70	$179.70
Purchase #2	$159.92	5.330%	$168.4437	$168.44	$168.45	$168.40
Purchase #3	$83.33	8.647%	$90.5355	$90.54	$90.55	$90.50
Purchase #4	$54.94	12.485%	$61.7993	$61.80	$61.80	$61.80
Purchase #5	$183.53	8.372%	$198.8951	$198.90	$198.90	$198.90
Purchase #6	$104.32	11.767%	$116.5953	$116.60	$116.60	$116.60
Purchase #7	$90.79	3.327%	$93.8106	$93.81	$93.80	$93.80
7 purchase totals =	$848.77		$909.7706	$909.78	$909.80	$909.70