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	$182.58	3.284%	$188.5759	$188.58	$188.60	$188.60
Purchase #2	$51.47	3.828%	$53.4403	$53.44	$53.45	$53.40
Purchase #3	$202.64	9.456%	$221.8016	$221.80	$221.80	$221.80
Purchase #4	$131.53	7.617%	$141.5486	$141.55	$141.55	$141.50
Purchase #5	$119.25	3.224%	$123.0946	$123.09	$123.10	$123.10
Purchase #6	$191.83	9.782%	$210.5948	$210.59	$210.60	$210.60
Purchase #7	$221.28	12.651%	$249.2741	$249.27	$249.25	$249.30
7 purchase totals =	$1,100.58		$1,188.3299	$1,188.32	$1,188.35	$1,188.30