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	$176.90	6.390%	$188.2039	$188.20	$188.20	$188.20
Purchase #2	$210.91	7.593%	$226.9244	$226.92	$226.90	$226.90
Purchase #3	$93.69	10.356%	$103.3925	$103.39	$103.40	$103.40
Purchase #4	$78.73	7.265%	$84.4497	$84.45	$84.45	$84.40
Purchase #5	$174.90	9.158%	$190.9173	$190.92	$190.90	$190.90
Purchase #6	$77.54	5.612%	$81.8915	$81.89	$81.90	$81.90
Purchase #7	$250.38	11.529%	$279.2463	$279.25	$279.25	$279.20
7 purchase totals =	$1,063.05		$1,155.0256	$1,155.02	$1,155.00	$1,154.90