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	$40.51	4.702%	$42.4148	$42.41	$42.40	$42.40
Purchase #2	$94.77	13.823%	$107.8701	$107.87	$107.85	$107.90
Purchase #3	$225.29	8.809%	$245.1358	$245.14	$245.15	$245.10
Purchase #4	$130.32	7.206%	$139.7109	$139.71	$139.70	$139.70
Purchase #5	$77.90	11.438%	$86.8102	$86.81	$86.80	$86.80
Purchase #6	$56.59	5.692%	$59.8111	$59.81	$59.80	$59.80
Purchase #7	$169.38	5.397%	$178.5214	$178.52	$178.50	$178.50
7 purchase totals =	$794.76		$860.2743	$860.27	$860.20	$860.20