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	$19.62	4.523%	$20.5074	$20.51	$20.50	$20.50
Purchase #2	$104.26	11.330%	$116.0727	$116.07	$116.05	$116.10
Purchase #3	$28.25	10.655%	$31.26	$31.26	$31.25	$31.30
Purchase #4	$212.82	3.740%	$220.7795	$220.78	$220.80	$220.80
Purchase #5	$70.59	3.593%	$73.1263	$73.13	$73.15	$73.10
Purchase #6	$51.63	3.181%	$53.2724	$53.27	$53.25	$53.30
Purchase #7	$39.28	10.208%	$43.2897	$43.29	$43.30	$43.30
7 purchase totals =	$526.45		$558.3080	$558.31	$558.30	$558.40