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	$14.38	9.315%	$15.7195	$15.72	$15.70	$15.70
Purchase #2	$122.45	4.837%	$128.3729	$128.37	$128.35	$128.40
Purchase #3	$101.87	11.286%	$113.367	$113.37	$113.35	$113.40
Purchase #4	$151.50	11.117%	$168.3423	$168.34	$168.35	$168.30
Purchase #5	$157.94	13.441%	$179.1687	$179.17	$179.15	$179.20
Purchase #6	$72.67	8.696%	$78.9894	$78.99	$79.00	$79.00
Purchase #7	$94.35	11.374%	$105.0814	$105.08	$105.10	$105.10
7 purchase totals =	$715.16		$789.0412	$789.04	$789.00	$789.10