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	$81.92	10.576%	$90.5839	$90.58	$90.60	$90.60
Purchase #2	$91.43	10.740%	$101.2496	$101.25	$101.25	$101.20
Purchase #3	$82.96	7.835%	$89.4599	$89.46	$89.45	$89.50
Purchase #4	$64.68	3.643%	$67.0363	$67.04	$67.05	$67.00
Purchase #5	$90.64	8.627%	$98.4595	$98.46	$98.45	$98.50
Purchase #6	$198.96	9.750%	$218.3586	$218.36	$218.35	$218.40
Purchase #7	$35.88	7.534%	$38.5832	$38.58	$38.60	$38.60
7 purchase totals =	$646.47		$703.7310	$703.73	$703.75	$703.80