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	$191.35	9.796%	$210.0946	$210.09	$210.10	$210.10
Purchase #2	$91.84	12.662%	$103.4688	$103.47	$103.45	$103.50
Purchase #3	$199.72	5.799%	$211.3018	$211.30	$211.30	$211.30
Purchase #4	$38.49	9.814%	$42.2674	$42.27	$42.25	$42.30
Purchase #5	$149.99	9.709%	$164.5525	$164.55	$164.55	$164.60
Purchase #6	$30.68	9.228%	$33.5112	$33.51	$33.50	$33.50
Purchase #7	$217.51	7.852%	$234.5889	$234.59	$234.60	$234.60
7 purchase totals =	$919.58		$999.7852	$999.78	$999.75	$999.90