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	$223.59	12.243%	$250.9641	$250.96	$250.95	$251.00
Purchase #2	$18.99	5.247%	$19.9864	$19.99	$20.00	$20.00
Purchase #3	$127.72	11.404%	$142.2852	$142.29	$142.30	$142.30
Purchase #4	$6.88	9.592%	$7.5399	$7.54	$7.55	$7.50
Purchase #5	$105.37	6.275%	$111.982	$111.98	$112.00	$112.00
Purchase #6	$170.68	10.105%	$187.9272	$187.93	$187.95	$187.90
Purchase #7	$90.49	8.212%	$97.921	$97.92	$97.90	$97.90
7 purchase totals =	$743.72		$818.6058	$818.61	$818.65	$818.60