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	$179.83	3.492%	$186.1097	$186.11	$186.10	$186.10
Purchase #2	$161.64	6.314%	$171.8459	$171.85	$171.85	$171.80
Purchase #3	$107.59	10.547%	$118.9375	$118.94	$118.95	$118.90
Purchase #4	$188.28	6.410%	$200.3487	$200.35	$200.35	$200.30
Purchase #5	$125.88	4.749%	$131.858	$131.86	$131.85	$131.90
Purchase #6	$176.90	12.827%	$199.591	$199.59	$199.60	$199.60
Purchase #7	$124.91	7.830%	$134.6905	$134.69	$134.70	$134.70
7 purchase totals =	$1,065.03		$1,143.3813	$1,143.39	$1,143.40	$1,143.30