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	$186.36	6.861%	$199.1462	$199.15	$199.15	$199.10
Purchase #2	$146.26	6.697%	$156.055	$156.06	$156.05	$156.10
Purchase #3	$120.85	9.860%	$132.7658	$132.77	$132.75	$132.80
Purchase #4	$68.48	7.743%	$73.7824	$73.78	$73.80	$73.80
Purchase #5	$38.86	5.223%	$40.8897	$40.89	$40.90	$40.90
Purchase #6	$78.25	5.354%	$82.4395	$82.44	$82.45	$82.40
Purchase #7	$163.47	3.625%	$169.3958	$169.40	$169.40	$169.40
7 purchase totals =	$802.53		$854.4744	$854.49	$854.50	$854.50