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	$207.36	10.378%	$228.8798	$228.88	$228.90	$228.90
Purchase #2	$33.44	4.245%	$34.8595	$34.86	$34.85	$34.90
Purchase #3	$101.69	6.392%	$108.19	$108.19	$108.20	$108.20
Purchase #4	$75.66	3.634%	$78.4095	$78.41	$78.40	$78.40
Purchase #5	$109.67	12.624%	$123.5147	$123.51	$123.50	$123.50
Purchase #6	$224.26	13.856%	$255.3335	$255.33	$255.35	$255.30
Purchase #7	$78.34	6.748%	$83.6264	$83.63	$83.65	$83.60
7 purchase totals =	$830.42		$912.8134	$912.81	$912.85	$912.80