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	$234.63	7.238%	$251.6125	$251.61	$251.60	$251.60
Purchase #2	$101.73	8.842%	$110.725	$110.73	$110.75	$110.70
Purchase #3	$158.45	4.425%	$165.4614	$165.46	$165.45	$165.50
Purchase #4	$89.71	5.615%	$94.7472	$94.75	$94.75	$94.70
Purchase #5	$62.72	7.425%	$67.377	$67.38	$67.40	$67.40
Purchase #6	$113.50	8.799%	$123.4869	$123.49	$123.50	$123.50
Purchase #7	$81.69	13.187%	$92.4625	$92.46	$92.45	$92.50
7 purchase totals =	$842.43		$905.8725	$905.88	$905.90	$905.90