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	$40.76	7.687%	$43.8932	$43.89	$43.90	$43.90
Purchase #2	$109.39	6.748%	$116.7716	$116.77	$116.75	$116.80
Purchase #3	$232.44	5.243%	$244.6268	$244.63	$244.65	$244.60
Purchase #4	$77.89	3.361%	$80.5079	$80.51	$80.50	$80.50
Purchase #5	$241.46	7.630%	$259.8834	$259.88	$259.90	$259.90
Purchase #6	$146.56	4.349%	$152.9339	$152.93	$152.95	$152.90
Purchase #7	$237.35	3.743%	$246.234	$246.23	$246.25	$246.20
7 purchase totals =	$1,085.85		$1,144.8508	$1,144.84	$1,144.90	$1,144.80