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	$118.81	3.717%	$123.2262	$123.23	$123.25	$123.20
Purchase #2	$210.69	5.289%	$221.8334	$221.83	$221.85	$221.80
Purchase #3	$190.56	5.142%	$200.3586	$200.36	$200.35	$200.40
Purchase #4	$48.47	7.413%	$52.0631	$52.06	$52.05	$52.10
Purchase #5	$88.42	3.523%	$91.535	$91.54	$91.55	$91.50
Purchase #6	$108.99	4.175%	$113.5403	$113.54	$113.55	$113.50
Purchase #7	$156.82	13.148%	$177.4387	$177.44	$177.45	$177.40
7 purchase totals =	$922.76		$979.9953	$980.00	$980.05	$979.90