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	$13.68	13.693%	$15.5532	$15.55	$15.55	$15.60
Purchase #2	$244.87	8.274%	$265.1305	$265.13	$265.15	$265.10
Purchase #3	$31.80	4.629%	$33.272	$33.27	$33.25	$33.30
Purchase #4	$222.38	13.800%	$253.0684	$253.07	$253.05	$253.10
Purchase #5	$65.79	9.222%	$71.8572	$71.86	$71.85	$71.90
Purchase #6	$85.61	9.580%	$93.8114	$93.81	$93.80	$93.80
Purchase #7	$68.53	5.407%	$72.2354	$72.24	$72.25	$72.20
7 purchase totals =	$732.66		$804.9281	$804.93	$804.90	$805.00