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	$35.60	11.741%	$39.7798	$39.78	$39.80	$39.80
Purchase #2	$30.60	4.349%	$31.9308	$31.93	$31.95	$31.90
Purchase #3	$86.85	6.604%	$92.5856	$92.59	$92.60	$92.60
Purchase #4	$246.84	8.318%	$267.3722	$267.37	$267.35	$267.40
Purchase #5	$141.86	4.529%	$148.2848	$148.28	$148.30	$148.30
Purchase #6	$189.77	3.377%	$196.1785	$196.18	$196.20	$196.20
Purchase #7	$28.27	4.162%	$29.4466	$29.45	$29.45	$29.40
7 purchase totals =	$759.79		$805.5783	$805.58	$805.65	$805.60