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	$131.37	4.759%	$137.6219	$137.62	$137.60	$137.60
Purchase #2	$234.32	12.766%	$264.2333	$264.23	$264.25	$264.20
Purchase #3	$115.83	10.591%	$128.0976	$128.10	$128.10	$128.10
Purchase #4	$226.64	5.358%	$238.7834	$238.78	$238.80	$238.80
Purchase #5	$187.44	6.208%	$199.0763	$199.08	$199.10	$199.10
Purchase #6	$78.96	11.799%	$88.2765	$88.28	$88.30	$88.30
Purchase #7	$116.65	9.557%	$127.7982	$127.80	$127.80	$127.80
7 purchase totals =	$1,091.21		$1,183.8872	$1,183.89	$1,183.95	$1,183.90