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	$100.94	10.681%	$111.7214	$111.72	$111.70	$111.70
Purchase #2	$28.26	12.805%	$31.8787	$31.88	$31.90	$31.90
Purchase #3	$52.28	11.292%	$58.1835	$58.18	$58.20	$58.20
Purchase #4	$36.80	8.585%	$39.9593	$39.96	$39.95	$40.00
Purchase #5	$69.71	4.481%	$72.8337	$72.83	$72.85	$72.80
Purchase #6	$174.90	3.698%	$181.3678	$181.37	$181.35	$181.40
Purchase #7	$138.38	4.319%	$144.3566	$144.36	$144.35	$144.40
7 purchase totals =	$601.27		$640.3010	$640.30	$640.30	$640.40