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	$18.51	10.624%	$20.4765	$20.48	$20.50	$20.50
Purchase #2	$115.34	3.456%	$119.3262	$119.33	$119.35	$119.30
Purchase #3	$36.75	13.270%	$41.6267	$41.63	$41.65	$41.60
Purchase #4	$124.28	5.871%	$131.5765	$131.58	$131.60	$131.60
Purchase #5	$187.65	3.487%	$194.1934	$194.19	$194.20	$194.20
Purchase #6	$100.90	8.148%	$109.1213	$109.12	$109.10	$109.10
Purchase #7	$117.73	9.149%	$128.5011	$128.50	$128.50	$128.50
7 purchase totals =	$701.16		$744.8217	$744.83	$744.90	$744.80