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	$55.42	7.521%	$59.5881	$59.59	$59.60	$59.60
Purchase #2	$94.50	9.399%	$103.3821	$103.38	$103.40	$103.40
Purchase #3	$179.79	5.189%	$189.1193	$189.12	$189.10	$189.10
Purchase #4	$88.53	4.488%	$92.5032	$92.50	$92.50	$92.50
Purchase #5	$21.77	3.567%	$22.5465	$22.55	$22.55	$22.50
Purchase #6	$222.50	8.424%	$241.2434	$241.24	$241.25	$241.20
Purchase #7	$61.57	5.261%	$64.8092	$64.81	$64.80	$64.80
7 purchase totals =	$724.08		$773.1918	$773.19	$773.20	$773.10