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	$171.54	3.732%	$177.9419	$177.94	$177.95	$177.90
Purchase #2	$182.55	8.789%	$198.5943	$198.59	$198.60	$198.60
Purchase #3	$131.91	8.832%	$143.5603	$143.56	$143.55	$143.60
Purchase #4	$83.94	3.470%	$86.8527	$86.85	$86.85	$86.90
Purchase #5	$50.28	11.394%	$56.0089	$56.01	$56.00	$56.00
Purchase #6	$142.62	5.835%	$150.9419	$150.94	$150.95	$150.90
Purchase #7	$18.88	4.314%	$19.6945	$19.69	$19.70	$19.70
7 purchase totals =	$781.72		$833.5945	$833.58	$833.60	$833.60