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	$50.76	4.787%	$53.1899	$53.19	$53.20	$53.20
Purchase #2	$68.94	5.419%	$72.6759	$72.68	$72.70	$72.70
Purchase #3	$237.57	8.121%	$256.8631	$256.86	$256.85	$256.90
Purchase #4	$130.39	11.554%	$145.4553	$145.46	$145.45	$145.50
Purchase #5	$107.61	13.451%	$122.0846	$122.08	$122.10	$122.10
Purchase #6	$39.36	9.374%	$43.0496	$43.05	$43.05	$43.00
Purchase #7	$87.46	3.558%	$90.5718	$90.57	$90.55	$90.60
7 purchase totals =	$722.09		$783.8902	$783.89	$783.90	$784.00