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	$51.69	3.575%	$53.5379	$53.54	$53.55	$53.50
Purchase #2	$90.98	13.276%	$103.0585	$103.06	$103.05	$103.10
Purchase #3	$165.65	10.177%	$182.5082	$182.51	$182.50	$182.50
Purchase #4	$65.89	13.855%	$75.0191	$75.02	$75.00	$75.00
Purchase #5	$34.55	8.592%	$37.5185	$37.52	$37.50	$37.50
Purchase #6	$247.63	13.831%	$281.8797	$281.88	$281.90	$281.90
Purchase #7	$28.86	8.153%	$31.213	$31.21	$31.20	$31.20
7 purchase totals =	$685.25		$764.7349	$764.74	$764.70	$764.70