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	$110.32	10.489%	$121.8915	$121.89	$121.90	$121.90
Purchase #2	$188.32	4.297%	$196.4121	$196.41	$196.40	$196.40
Purchase #3	$38.31	9.828%	$42.0751	$42.08	$42.10	$42.10
Purchase #4	$212.82	9.620%	$233.2933	$233.29	$233.30	$233.30
Purchase #5	$40.71	10.422%	$44.9528	$44.95	$44.95	$45.00
Purchase #6	$107.97	5.284%	$113.6751	$113.68	$113.70	$113.70
Purchase #7	$118.51	7.185%	$127.0249	$127.02	$127.00	$127.00
7 purchase totals =	$816.96		$879.3248	$879.32	$879.35	$879.40