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	$29.68	8.143%	$32.0968	$32.10	$32.10	$32.10
Purchase #2	$162.85	3.201%	$168.0628	$168.06	$168.05	$168.10
Purchase #3	$161.33	6.661%	$172.0762	$172.08	$172.10	$172.10
Purchase #4	$163.67	7.768%	$176.3839	$176.38	$176.40	$176.40
Purchase #5	$181.83	12.423%	$204.4187	$204.42	$204.40	$204.40
Purchase #6	$246.57	7.705%	$265.5682	$265.57	$265.55	$265.60
Purchase #7	$69.79	3.838%	$72.4685	$72.47	$72.45	$72.50
7 purchase totals =	$1,015.72		$1,091.0751	$1,091.08	$1,091.05	$1,091.20