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	$198.40	3.605%	$205.5523	$205.55	$205.55	$205.60
Purchase #2	$59.38	5.111%	$62.4149	$62.41	$62.40	$62.40
Purchase #3	$119.40	7.291%	$128.1055	$128.11	$128.10	$128.10
Purchase #4	$155.52	11.273%	$173.0518	$173.05	$173.05	$173.10
Purchase #5	$5.45	8.595%	$5.9184	$5.92	$5.90	$5.90
Purchase #6	$39.44	7.597%	$42.4363	$42.44	$42.45	$42.40
Purchase #7	$156.88	9.455%	$171.713	$171.71	$171.70	$171.70
7 purchase totals =	$734.47		$789.1922	$789.19	$789.15	$789.20