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	$13.76	10.260%	$15.1718	$15.17	$15.15	$15.20
Purchase #2	$37.93	4.871%	$39.7776	$39.78	$39.80	$39.80
Purchase #3	$181.33	5.779%	$191.8091	$191.81	$191.80	$191.80
Purchase #4	$94.55	10.121%	$104.1194	$104.12	$104.10	$104.10
Purchase #5	$77.59	10.177%	$85.4863	$85.49	$85.50	$85.50
Purchase #6	$225.29	13.407%	$255.4946	$255.49	$255.50	$255.50
Purchase #7	$74.97	6.423%	$79.7853	$79.79	$79.80	$79.80
7 purchase totals =	$705.42		$771.6441	$771.65	$771.65	$771.70