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	$204.72	9.673%	$224.5226	$224.52	$224.50	$224.50
Purchase #2	$172.73	4.607%	$180.6877	$180.69	$180.70	$180.70
Purchase #3	$209.86	9.857%	$230.5459	$230.55	$230.55	$230.50
Purchase #4	$41.97	3.480%	$43.4306	$43.43	$43.45	$43.40
Purchase #5	$222.52	4.190%	$231.8436	$231.84	$231.85	$231.80
Purchase #6	$114.38	11.454%	$127.4811	$127.48	$127.50	$127.50
Purchase #7	$188.92	3.135%	$194.8426	$194.84	$194.85	$194.80
7 purchase totals =	$1,155.10		$1,233.3541	$1,233.35	$1,233.40	$1,233.20