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	$106.79	11.327%	$118.8861	$118.89	$118.90	$118.90
Purchase #2	$74.27	8.534%	$80.6082	$80.61	$80.60	$80.60
Purchase #3	$48.57	10.831%	$53.8306	$53.83	$53.85	$53.80
Purchase #4	$105.76	3.156%	$109.0978	$109.10	$109.10	$109.10
Purchase #5	$90.46	3.550%	$93.6713	$93.67	$93.65	$93.70
Purchase #6	$163.78	12.359%	$184.0216	$184.02	$184.00	$184.00
Purchase #7	$24.42	11.716%	$27.281	$27.28	$27.30	$27.30
7 purchase totals =	$614.05		$667.3966	$667.40	$667.40	$667.40