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	$128.86	13.114%	$145.7587	$145.76	$145.75	$145.80
Purchase #2	$187.80	13.380%	$212.9276	$212.93	$212.95	$212.90
Purchase #3	$226.71	7.283%	$243.2213	$243.22	$243.20	$243.20
Purchase #4	$207.52	12.233%	$232.9059	$232.91	$232.90	$232.90
Purchase #5	$127.78	9.811%	$140.3165	$140.32	$140.30	$140.30
Purchase #6	$192.89	3.728%	$200.0809	$200.08	$200.10	$200.10
Purchase #7	$98.33	7.308%	$105.516	$105.52	$105.50	$105.50
7 purchase totals =	$1,169.89		$1,280.7269	$1,280.74	$1,280.70	$1,280.70