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	$108.40	6.419%	$115.3582	$115.36	$115.35	$115.40
Purchase #2	$97.61	3.315%	$100.8458	$100.85	$100.85	$100.80
Purchase #3	$8.89	13.648%	$10.1033	$10.10	$10.10	$10.10
Purchase #4	$40.75	11.592%	$45.4737	$45.47	$45.45	$45.50
Purchase #5	$25.98	11.554%	$28.9817	$28.98	$29.00	$29.00
Purchase #6	$94.37	8.592%	$102.4783	$102.48	$102.50	$102.50
Purchase #7	$124.85	6.275%	$132.6843	$132.68	$132.70	$132.70
7 purchase totals =	$500.85		$535.9253	$535.92	$535.95	$536.00