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	$15.90	9.753%	$17.4507	$17.45	$17.45	$17.50
Purchase #2	$93.95	5.745%	$99.3474	$99.35	$99.35	$99.30
Purchase #3	$196.51	6.211%	$208.7152	$208.72	$208.70	$208.70
Purchase #4	$19.90	8.111%	$21.5141	$21.51	$21.50	$21.50
Purchase #5	$42.84	10.761%	$47.45	$47.45	$47.45	$47.50
Purchase #6	$70.71	3.372%	$73.0943	$73.09	$73.10	$73.10
Purchase #7	$196.33	7.187%	$210.4402	$210.44	$210.45	$210.40
7 purchase totals =	$636.14		$678.0119	$678.01	$678.00	$678.00