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	$26.38	11.773%	$29.4857	$29.49	$29.50	$29.50
Purchase #2	$96.42	4.455%	$100.7155	$100.72	$100.70	$100.70
Purchase #3	$214.83	7.708%	$231.3891	$231.39	$231.40	$231.40
Purchase #4	$100.64	10.676%	$111.3843	$111.38	$111.40	$111.40
Purchase #5	$196.43	3.449%	$203.2049	$203.20	$203.20	$203.20
Purchase #6	$211.54	9.380%	$231.3825	$231.38	$231.40	$231.40
Purchase #7	$85.50	9.154%	$93.3267	$93.33	$93.35	$93.30
7 purchase totals =	$931.74		$1,000.8887	$1,000.89	$1,000.95	$1,000.90