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	$94.92	11.759%	$106.0816	$106.08	$106.10	$106.10
Purchase #2	$225.74	10.338%	$249.077	$249.08	$249.10	$249.10
Purchase #3	$25.86	11.447%	$28.8202	$28.82	$28.80	$28.80
Purchase #4	$192.53	11.263%	$214.2147	$214.21	$214.20	$214.20
Purchase #5	$52.71	12.477%	$59.2866	$59.29	$59.30	$59.30
Purchase #6	$78.79	13.702%	$89.5858	$89.59	$89.60	$89.60
Purchase #7	$105.58	7.689%	$113.698	$113.70	$113.70	$113.70
7 purchase totals =	$776.13		$860.7639	$860.77	$860.80	$860.80