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	$89.49	12.378%	$100.5671	$100.57	$100.55	$100.60
Purchase #2	$38.86	8.697%	$42.2397	$42.24	$42.25	$42.20
Purchase #3	$142.48	11.236%	$158.4891	$158.49	$158.50	$158.50
Purchase #4	$106.85	9.161%	$116.6385	$116.64	$116.65	$116.60
Purchase #5	$165.35	10.277%	$182.343	$182.34	$182.35	$182.30
Purchase #6	$72.34	7.702%	$77.9116	$77.91	$77.90	$77.90
Purchase #7	$52.80	10.181%	$58.1756	$58.18	$58.20	$58.20
7 purchase totals =	$668.17		$736.3646	$736.37	$736.40	$736.30