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	$78.91	5.238%	$83.0433	$83.04	$83.05	$83.00
Purchase #2	$120.94	3.178%	$124.7835	$124.78	$124.80	$124.80
Purchase #3	$102.86	10.299%	$113.4536	$113.45	$113.45	$113.50
Purchase #4	$45.57	9.845%	$50.0564	$50.06	$50.05	$50.10
Purchase #5	$170.69	4.872%	$179.006	$179.01	$179.00	$179.00
Purchase #6	$132.93	3.745%	$137.9082	$137.91	$137.90	$137.90
Purchase #7	$40.42	5.460%	$42.6269	$42.63	$42.65	$42.60
7 purchase totals =	$692.32		$730.8779	$730.88	$730.90	$730.90