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	$220.36	6.374%	$234.4057	$234.41	$234.40	$234.40
Purchase #2	$150.47	10.705%	$166.5778	$166.58	$166.60	$166.60
Purchase #3	$67.96	7.276%	$72.9048	$72.90	$72.90	$72.90
Purchase #4	$29.45	6.717%	$31.4282	$31.43	$31.45	$31.40
Purchase #5	$177.73	7.371%	$190.8305	$190.83	$190.85	$190.80
Purchase #6	$94.73	10.502%	$104.6785	$104.68	$104.70	$104.70
Purchase #7	$55.46	7.247%	$59.4792	$59.48	$59.50	$59.50
7 purchase totals =	$796.16		$860.3047	$860.31	$860.40	$860.30