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	$133.89	13.125%	$151.4631	$151.46	$151.45	$151.50
Purchase #2	$136.71	4.246%	$142.5147	$142.51	$142.50	$142.50
Purchase #3	$18.57	3.183%	$19.1611	$19.16	$19.15	$19.20
Purchase #4	$42.76	10.587%	$47.287	$47.29	$47.30	$47.30
Purchase #5	$64.84	9.357%	$70.9071	$70.91	$70.90	$70.90
Purchase #6	$163.32	11.428%	$181.9842	$181.98	$182.00	$182.00
Purchase #7	$159.43	10.277%	$175.8146	$175.81	$175.80	$175.80
7 purchase totals =	$719.52		$789.1318	$789.12	$789.10	$789.20