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	$80.82	12.453%	$90.8845	$90.88	$90.90	$90.90
Purchase #2	$19.59	11.289%	$21.8015	$21.80	$21.80	$21.80
Purchase #3	$10.64	11.520%	$11.8657	$11.87	$11.85	$11.90
Purchase #4	$246.49	3.159%	$254.2766	$254.28	$254.30	$254.30
Purchase #5	$230.25	11.765%	$257.3389	$257.34	$257.35	$257.30
Purchase #6	$244.97	10.534%	$270.7751	$270.78	$270.80	$270.80
Purchase #7	$42.54	6.617%	$45.3549	$45.35	$45.35	$45.40
7 purchase totals =	$875.30		$952.2972	$952.30	$952.35	$952.40