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	$81.77	10.483%	$90.3419	$90.34	$90.35	$90.30
Purchase #2	$59.93	9.779%	$65.7906	$65.79	$65.80	$65.80
Purchase #3	$196.49	7.174%	$210.5862	$210.59	$210.60	$210.60
Purchase #4	$61.49	7.696%	$66.2223	$66.22	$66.20	$66.20
Purchase #5	$111.38	3.526%	$115.3073	$115.31	$115.30	$115.30
Purchase #6	$47.78	7.368%	$51.3004	$51.30	$51.30	$51.30
Purchase #7	$230.56	12.849%	$260.1847	$260.18	$260.20	$260.20
7 purchase totals =	$789.40		$859.7334	$859.73	$859.75	$859.70