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	$42.39	13.206%	$47.988	$47.99	$48.00	$48.00
Purchase #2	$220.45	10.459%	$243.5069	$243.51	$243.50	$243.50
Purchase #3	$16.89	11.645%	$18.8568	$18.86	$18.85	$18.90
Purchase #4	$89.37	12.553%	$100.5886	$100.59	$100.60	$100.60
Purchase #5	$110.90	4.143%	$115.4946	$115.49	$115.50	$115.50
Purchase #6	$167.76	5.121%	$176.351	$176.35	$176.35	$176.40
Purchase #7	$140.76	9.352%	$153.9239	$153.92	$153.90	$153.90
7 purchase totals =	$788.52		$856.7098	$856.71	$856.70	$856.80