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	$93.75	5.678%	$99.0731	$99.07	$99.05	$99.10
Purchase #2	$153.54	9.843%	$168.6529	$168.65	$168.65	$168.70
Purchase #3	$218.89	6.669%	$233.4878	$233.49	$233.50	$233.50
Purchase #4	$81.64	9.552%	$89.4383	$89.44	$89.45	$89.40
Purchase #5	$250.80	12.747%	$282.7695	$282.77	$282.75	$282.80
Purchase #6	$14.63	9.547%	$16.0267	$16.03	$16.05	$16.00
Purchase #7	$47.61	6.745%	$50.8213	$50.82	$50.80	$50.80
7 purchase totals =	$860.86		$940.2696	$940.27	$940.25	$940.30