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	$28.88	13.790%	$32.8626	$32.86	$32.85	$32.90
Purchase #2	$188.82	9.278%	$206.3387	$206.34	$206.35	$206.30
Purchase #3	$91.84	5.574%	$96.9592	$96.96	$96.95	$97.00
Purchase #4	$119.90	6.519%	$127.7163	$127.72	$127.70	$127.70
Purchase #5	$89.84	12.191%	$100.7924	$100.79	$100.80	$100.80
Purchase #6	$47.92	4.721%	$50.1823	$50.18	$50.20	$50.20
Purchase #7	$71.92	8.487%	$78.0239	$78.02	$78.00	$78.00
7 purchase totals =	$639.12		$692.8754	$692.87	$692.85	$692.90