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	$138.94	11.675%	$155.1612	$155.16	$155.15	$155.20
Purchase #2	$83.55	6.801%	$89.2322	$89.23	$89.25	$89.20
Purchase #3	$182.69	9.866%	$200.7142	$200.71	$200.70	$200.70
Purchase #4	$176.70	7.781%	$190.449	$190.45	$190.45	$190.40
Purchase #5	$196.64	7.725%	$211.8304	$211.83	$211.85	$211.80
Purchase #6	$65.65	9.258%	$71.7279	$71.73	$71.75	$71.70
Purchase #7	$45.63	13.850%	$51.9498	$51.95	$51.95	$51.90
7 purchase totals =	$889.80		$971.0647	$971.06	$971.10	$970.90