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	$9.88	6.345%	$10.5069	$10.51	$10.50	$10.50
Purchase #2	$23.77	5.767%	$25.1408	$25.14	$25.15	$25.10
Purchase #3	$126.45	12.656%	$142.4535	$142.45	$142.45	$142.50
Purchase #4	$11.72	4.696%	$12.2704	$12.27	$12.25	$12.30
Purchase #5	$248.82	6.871%	$265.9164	$265.92	$265.90	$265.90
Purchase #6	$72.64	6.592%	$77.4284	$77.43	$77.45	$77.40
Purchase #7	$97.33	3.154%	$100.3998	$100.40	$100.40	$100.40
7 purchase totals =	$590.61		$634.1162	$634.12	$634.10	$634.10