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	$79.61	3.552%	$82.4377	$82.44	$82.45	$82.40
Purchase #2	$221.27	4.745%	$231.7693	$231.77	$231.75	$231.80
Purchase #3	$44.49	3.193%	$45.9106	$45.91	$45.90	$45.90
Purchase #4	$54.55	9.670%	$59.825	$59.83	$59.85	$59.80
Purchase #5	$61.98	10.364%	$68.4036	$68.40	$68.40	$68.40
Purchase #6	$29.34	9.540%	$32.139	$32.14	$32.15	$32.10
Purchase #7	$227.31	11.512%	$253.4779	$253.48	$253.50	$253.50
7 purchase totals =	$718.55		$773.9631	$773.97	$774.00	$773.90