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	$249.31	5.588%	$263.2414	$263.24	$263.25	$263.20
Purchase #2	$51.30	13.650%	$58.3025	$58.30	$58.30	$58.30
Purchase #3	$34.88	3.648%	$36.1524	$36.15	$36.15	$36.20
Purchase #4	$160.48	5.226%	$168.8667	$168.87	$168.85	$168.90
Purchase #5	$90.70	5.346%	$95.5488	$95.55	$95.55	$95.50
Purchase #6	$119.38	9.468%	$130.6829	$130.68	$130.70	$130.70
Purchase #7	$226.82	12.683%	$255.5876	$255.59	$255.60	$255.60
7 purchase totals =	$932.87		$1,008.3823	$1,008.38	$1,008.40	$1,008.40