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	$134.92	3.496%	$139.6368	$139.64	$139.65	$139.60
Purchase #2	$112.46	5.342%	$118.4676	$118.47	$118.45	$118.50
Purchase #3	$72.95	3.614%	$75.5864	$75.59	$75.60	$75.60
Purchase #4	$171.97	13.478%	$195.1481	$195.15	$195.15	$195.10
Purchase #5	$61.95	10.154%	$68.2404	$68.24	$68.25	$68.20
Purchase #6	$131.89	8.671%	$143.3262	$143.33	$143.35	$143.30
Purchase #7	$53.62	11.230%	$59.6415	$59.64	$59.65	$59.60
7 purchase totals =	$739.76		$800.0470	$800.06	$800.10	$799.90