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	$137.29	12.380%	$154.2865	$154.29	$154.30	$154.30
Purchase #2	$97.50	6.532%	$103.8687	$103.87	$103.85	$103.90
Purchase #3	$237.60	12.587%	$267.5067	$267.51	$267.50	$267.50
Purchase #4	$249.94	10.708%	$276.7036	$276.70	$276.70	$276.70
Purchase #5	$91.58	8.629%	$99.4824	$99.48	$99.50	$99.50
Purchase #6	$83.77	7.322%	$89.9036	$89.90	$89.90	$89.90
Purchase #7	$181.41	4.105%	$188.8569	$188.86	$188.85	$188.90
7 purchase totals =	$1,079.09		$1,180.6084	$1,180.61	$1,180.60	$1,180.70