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	$123.75	4.757%	$129.6368	$129.64	$129.65	$129.60
Purchase #2	$140.37	7.774%	$151.2824	$151.28	$151.30	$151.30
Purchase #3	$11.89	5.732%	$12.5715	$12.57	$12.55	$12.60
Purchase #4	$137.63	3.839%	$142.9136	$142.91	$142.90	$142.90
Purchase #5	$146.45	5.172%	$154.0244	$154.02	$154.00	$154.00
Purchase #6	$176.90	3.398%	$182.9111	$182.91	$182.90	$182.90
Purchase #7	$143.90	5.354%	$151.6044	$151.60	$151.60	$151.60
7 purchase totals =	$880.89		$924.9442	$924.93	$924.90	$924.90