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	$225.68	12.823%	$254.6189	$254.62	$254.60	$254.60
Purchase #2	$168.54	4.745%	$176.5372	$176.54	$176.55	$176.50
Purchase #3	$76.66	4.852%	$80.3795	$80.38	$80.40	$80.40
Purchase #4	$177.55	10.554%	$196.2886	$196.29	$196.30	$196.30
Purchase #5	$66.76	8.261%	$72.275	$72.28	$72.30	$72.30
Purchase #6	$63.38	11.382%	$70.5939	$70.59	$70.60	$70.60
Purchase #7	$5.76	7.797%	$6.2091	$6.21	$6.20	$6.20
7 purchase totals =	$784.33		$856.9022	$856.91	$856.95	$856.90