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	$50.96	9.623%	$55.8639	$55.86	$55.85	$55.90
Purchase #2	$36.44	10.431%	$40.2411	$40.24	$40.25	$40.20
Purchase #3	$215.59	11.688%	$240.7882	$240.79	$240.80	$240.80
Purchase #4	$159.49	10.711%	$176.573	$176.57	$176.55	$176.60
Purchase #5	$90.98	6.180%	$96.6026	$96.60	$96.60	$96.60
Purchase #6	$226.82	13.586%	$257.6358	$257.64	$257.65	$257.60
Purchase #7	$120.65	11.599%	$134.6442	$134.64	$134.65	$134.60
7 purchase totals =	$900.93		$1,002.3488	$1,002.34	$1,002.35	$1,002.30