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	$234.42	6.287%	$249.158	$249.16	$249.15	$249.20
Purchase #2	$190.88	11.250%	$212.354	$212.35	$212.35	$212.40
Purchase #3	$200.38	11.684%	$223.7924	$223.79	$223.80	$223.80
Purchase #4	$38.27	10.805%	$42.4051	$42.41	$42.40	$42.40
Purchase #5	$95.48	5.587%	$100.8145	$100.81	$100.80	$100.80
Purchase #6	$229.90	6.790%	$245.5102	$245.51	$245.50	$245.50
Purchase #7	$153.51	8.585%	$166.6888	$166.69	$166.70	$166.70
7 purchase totals =	$1,142.84		$1,240.7230	$1,240.72	$1,240.70	$1,240.80