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	$230.72	5.417%	$243.2181	$243.22	$243.20	$243.20
Purchase #2	$108.86	8.629%	$118.2535	$118.25	$118.25	$118.30
Purchase #3	$79.70	12.343%	$89.5374	$89.54	$89.55	$89.50
Purchase #4	$98.93	12.639%	$111.4338	$111.43	$111.45	$111.40
Purchase #5	$44.70	9.430%	$48.9152	$48.92	$48.90	$48.90
Purchase #6	$163.69	7.758%	$176.3891	$176.39	$176.40	$176.40
Purchase #7	$94.33	8.240%	$102.1028	$102.10	$102.10	$102.10
7 purchase totals =	$820.93		$889.8499	$889.85	$889.85	$889.80