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	$250.33	11.183%	$278.3244	$278.32	$278.30	$278.30
Purchase #2	$27.44	12.243%	$30.7995	$30.80	$30.80	$30.80
Purchase #3	$185.77	10.176%	$204.674	$204.67	$204.65	$204.70
Purchase #4	$137.71	5.190%	$144.8571	$144.86	$144.85	$144.90
Purchase #5	$175.87	6.872%	$187.9558	$187.96	$187.95	$188.00
Purchase #6	$113.45	12.179%	$127.2671	$127.27	$127.25	$127.30
Purchase #7	$206.90	5.116%	$217.485	$217.49	$217.50	$217.50
7 purchase totals =	$1,097.47		$1,191.3629	$1,191.37	$1,191.30	$1,191.50