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	$186.34	5.462%	$196.5179	$196.52	$196.50	$196.50
Purchase #2	$109.76	9.307%	$119.9754	$119.98	$120.00	$120.00
Purchase #3	$116.59	12.854%	$131.5765	$131.58	$131.60	$131.60
Purchase #4	$103.63	7.208%	$111.0997	$111.10	$111.10	$111.10
Purchase #5	$124.40	5.206%	$130.8763	$130.88	$130.90	$130.90
Purchase #6	$211.43	6.338%	$224.8304	$224.83	$224.85	$224.80
Purchase #7	$72.28	13.278%	$81.8773	$81.88	$81.90	$81.90
7 purchase totals =	$924.43		$996.7535	$996.77	$996.85	$996.80